diff --git a/includes/ContentImport/ContentImporter.php b/includes/ContentImport/ContentImporter.php
index b6530ee3f..94f0b73a5 100644
--- a/includes/ContentImport/ContentImporter.php
+++ b/includes/ContentImport/ContentImporter.php
@@ -99,8 +99,12 @@ public function set_relations( Relations $relations ): void {
 	 * @return string[] The updated, if needed, data array.
 	 */
 	public function handle_import( array $data = array() ) {
+		if ( ! $this->pre_flight_check() ) {
+			return $data;
+		}
+
 		$sources = $this->parse_sources();
-		if ( ! $this->pre_flight_check() || false === $sources ) {
+		if ( null === $sources ) {
 			return $data;
 		}
 
@@ -176,21 +180,21 @@ protected function pre_flight_check() {
 	/**
 	 * Parses the source blog and post IDs from the $_POST array validating them.
 	 *
-	 * @return int[]|bool
+	 * @return array{0: int, 1: int}|null
 	 */
-	public function parse_sources() {
+	public function parse_sources(): ?array {
 		if ( ! MslsRequest::has_var( 'msls_import' ) ) {
-			return false;
+			return null;
 		}
 
 		$msls_import = MslsRequest::get_var( 'msls_import' );
-		$import_data = array_filter( explode( '|', trim( $msls_import ) ), 'is_numeric' );
+		$import_data = array_values( array_filter( explode( '|', trim( $msls_import ) ), 'is_numeric' ) );
 
 		if ( count( $import_data ) !== 2 ) {
-			return false;
+			return null;
 		}
 
-		return array_map( 'intval', $import_data );
+		return array( (int) $import_data[0], (int) $import_data[1] );
 	}
 
 	/**
@@ -198,12 +202,12 @@ public function parse_sources() {
 	 *
 	 * @return int
 	 */
-	protected function get_the_blog_post_ID( $blog_id ) {
+	protected function get_the_blog_post_ID( $blog_id ): int {
 		switch_to_blog( $blog_id );
 
 		$id = get_the_ID();
 
-		if ( ! empty( $id ) ) {
+		if ( false !== $id && ! empty( $id ) ) {
 			restore_current_blog();
 
 			return $id;
@@ -226,11 +230,11 @@ protected function get_the_blog_post_ID( $blog_id ) {
 	 * @param int                  $blog_id
 	 * @param array<string, mixed> $data
 	 *
-	 * @return bool|int
+	 * @return int
 	 */
-	protected function insert_blog_post( $blog_id, array $data = array() ) {
+	protected function insert_blog_post( $blog_id, array $data = array() ): int {
 		if ( empty( $data ) ) {
-			return false;
+			return 0;
 		}
 
 		switch_to_blog( $blog_id );
@@ -238,7 +242,7 @@ protected function insert_blog_post( $blog_id, array $data = array() ) {
 		if ( ! empty( $data['post_type'] ) && ! post_type_exists( $data['post_type'] ) ) {
 			restore_current_blog();
 
-			return false;
+			return 0;
 		}
 
 		$this->handle( false );
@@ -249,7 +253,7 @@ protected function insert_blog_post( $blog_id, array $data = array() ) {
 		}
 		$this->handle( true );
 
-		$this->has_created_post = $post_id > 0 ? $post_id : false;
+		$this->has_created_post = $post_id > 0 ? $post_id : 0;
 
 		restore_current_blog();
 
@@ -319,29 +323,29 @@ public function import_content( ImportCoordinates $import_coordinates, array $po
 			$importers = Map::instance()->make( $import_coordinates );
 		}
 
-		if ( is_null( $this->get_logger() ) ) {
-			$this->set_logger( new ImportLogger( $import_coordinates ) );
-		}
+		$logger = $this->logger ?? new ImportLogger( $import_coordinates );
+		$this->set_logger( $logger );
 
-		if ( is_null( $this->get_relations() ) ) {
-			$this->set_relations( new Relations( $import_coordinates ) );
-		}
+		$relations = $this->relations ?? new Relations( $import_coordinates );
+		$this->set_relations( $relations );
 
 		if ( ! empty( $importers ) ) {
 			$source_post_id = $import_coordinates->source_post_id;
 			$dest_lang      = $import_coordinates->dest_lang;
 			$dest_post_id   = $import_coordinates->dest_post_id;
-			$this->relations->should_create( MslsOptionsPost::create( $source_post_id ), $dest_lang, $dest_post_id );
+			$relations->should_create( MslsOptionsPost::create( $source_post_id ), $dest_lang, $dest_post_id );
 
 			foreach ( $importers as $key => $importer ) {
-				/** @var Importer $importer */
+				if ( ! $importer instanceof Importer ) {
+					continue;
+				}
 				$post_fields = $importer->import( $post_fields );
-				$this->logger->merge( $importer->get_logger() );
-				$this->relations->merge( $importer->get_relations() );
+				$logger->merge( $importer->get_logger() );
+				$relations->merge( $importer->get_relations() );
 			}
 
-			$this->relations->create();
-			$this->logger->save();
+			$relations->create();
+			$logger->save();
 		}
 
 		/**
@@ -353,7 +357,7 @@ public function import_content( ImportCoordinates $import_coordinates, array $po
 		 *
 		 * @since TBD
 		 */
-		do_action( self::MSLS_AFTER_IMPORT_ACTION, $import_coordinates, $this->logger, $this->relations );
+		do_action( self::MSLS_AFTER_IMPORT_ACTION, $import_coordinates, $logger, $relations );
 
 		/**
 		 * Filters the data after the import ran.
@@ -367,8 +371,8 @@ public function import_content( ImportCoordinates $import_coordinates, array $po
 			'msls_content_import_data_after_import',
 			$post_fields,
 			$import_coordinates,
-			$this->logger,
-			$this->relations
+			$logger,
+			$relations
 		);
 	}
 
@@ -395,7 +399,7 @@ protected function update_inserted_blog_post_data( $blog_id, $post_id, array $da
 	 */
 	protected function redirect_to_blog_post( $dest_blog_id, $post_id ) {
 		switch_to_blog( $dest_blog_id );
-		$edit_post_link = html_entity_decode( get_edit_post_link( $post_id ) );
+		$edit_post_link = html_entity_decode( get_edit_post_link( $post_id ) ?? '' );
 		wp_safe_redirect( $edit_post_link );
 		die();
 	}
diff --git a/includes/ContentImport/ImportCoordinates.php b/includes/ContentImport/ImportCoordinates.php
index 12c3d46fb..9a18455cf 100644
--- a/includes/ContentImport/ImportCoordinates.php
+++ b/includes/ContentImport/ImportCoordinates.php
@@ -97,7 +97,14 @@ public function parse_importers_from_request(): void {
 			}
 		}
 
+		if ( ! is_array( $importers ) ) {
+			return;
+		}
+
 		foreach ( $importers as $importer_type => $slug ) {
+			if ( ! is_string( $slug ) ) {
+				continue;
+			}
 			$this->set_importer_for( $importer_type, $slug );
 		}
 	}
diff --git a/includes/ContentImport/ImportLogger.php b/includes/ContentImport/ImportLogger.php
index 23d6749f3..c510fab4b 100644
--- a/includes/ContentImport/ImportLogger.php
+++ b/includes/ContentImport/ImportLogger.php
@@ -8,7 +8,7 @@
 class ImportLogger {
 
 	/**
-	 * @var string
+	 * @var non-empty-string
 	 */
 	protected string $levels_delimiter = '/';
 
@@ -154,9 +154,9 @@ public function get_levels_delimiter(): string {
 	/**
 	 * Sets the string that will be used to split paths into levels.
 	 *
-	 * @param string $levels_delimiter
+	 * @param non-empty-string $levels_delimiter
 	 */
-	public function set_levels_delimiter( $levels_delimiter ): void {
+	public function set_levels_delimiter( string $levels_delimiter ): void {
 		$this->levels_delimiter = $levels_delimiter;
 	}
 
@@ -197,9 +197,17 @@ public function get_error( $where ) {
 	protected function get_nested_value( $where ) {
 		$path = $this->build_path( $where );
 
-		$data = $this->data[ array_shift( $path ) ];
+		$first = array_shift( $path );
+		if ( null === $first || ! isset( $this->data[ $first ] ) ) {
+			return null;
+		}
+
+		$data = $this->data[ $first ];
 
 		foreach ( $path as $frag ) {
+			if ( ! is_array( $data ) || ! isset( $data[ $frag ] ) ) {
+				return null;
+			}
 			$data = $data[ $frag ];
 		}
 
diff --git a/includes/ContentImport/Importers/AttachmentsImporters.php b/includes/ContentImport/Importers/AttachmentsImporters.php
index f1f333993..96947764d 100644
--- a/includes/ContentImport/Importers/AttachmentsImporters.php
+++ b/includes/ContentImport/Importers/AttachmentsImporters.php
@@ -9,7 +9,7 @@ class AttachmentsImporters extends ImportersBaseFactory {
 	const TYPE = 'attachments';
 
 	/**
-	 * @var array<string, string>
+	 * @var array<string, class-string<Importer>>
 	 */
 	protected array $importers_map = array(
 		Linking::TYPE => Linking::class,
diff --git a/includes/ContentImport/Importers/ImportersBaseFactory.php b/includes/ContentImport/Importers/ImportersBaseFactory.php
index 122d316af..885de3496 100644
--- a/includes/ContentImport/Importers/ImportersBaseFactory.php
+++ b/includes/ContentImport/Importers/ImportersBaseFactory.php
@@ -13,7 +13,7 @@ abstract class ImportersBaseFactory extends MslsRegistryInstance implements Impo
 	const TYPE = 'none';
 
 	/**
-	 * @var array<string, string> An array defining the slug and Importer class relationships in
+	 * @var array<string, class-string<Importer>> An array defining the slug and Importer class relationships in
 	 *            the shape [ <slug> => <importer-class> ]
 	 */
 	protected array $importers_map = array();
@@ -67,6 +67,9 @@ public function make( ImportCoordinates $import_coordinates ) {
 
 		// If there is some incoherence, return the null-doing base importer.
 		$class = ! empty( $slug ) && isset( $map[ $slug ] ) ? $map[ $slug ] : BaseImporter::class;
+		if ( ! is_string( $class ) || ! is_a( $class, Importer::class, true ) ) {
+			$class = BaseImporter::class;
+		}
 
 		return new $class( $import_coordinates );
 	}
diff --git a/includes/ContentImport/Importers/PostFieldsImporters.php b/includes/ContentImport/Importers/PostFieldsImporters.php
index 2e0d989e9..7313b786e 100644
--- a/includes/ContentImport/Importers/PostFieldsImporters.php
+++ b/includes/ContentImport/Importers/PostFieldsImporters.php
@@ -9,7 +9,7 @@ class PostFieldsImporters extends ImportersBaseFactory {
 	const TYPE = 'post-fields';
 
 	/**
-	 * @var array<string, string>
+	 * @var array<string, class-string<Importer>>
 	 */
 	protected array $importers_map = array(
 		Duplicating::TYPE => Duplicating::class,
diff --git a/includes/ContentImport/Importers/PostMetaImporters.php b/includes/ContentImport/Importers/PostMetaImporters.php
index 8930ff9dd..4d7de1bc5 100644
--- a/includes/ContentImport/Importers/PostMetaImporters.php
+++ b/includes/ContentImport/Importers/PostMetaImporters.php
@@ -9,7 +9,7 @@ class PostMetaImporters extends ImportersBaseFactory {
 	const TYPE = 'post-meta';
 
 	/**
-	 * @var array<string, string>
+	 * @var array<string, class-string<Importer>>
 	 */
 	protected array $importers_map = array(
 		Duplicating::TYPE => Duplicating::class,
diff --git a/includes/ContentImport/Importers/PostThumbnail/Linking.php b/includes/ContentImport/Importers/PostThumbnail/Linking.php
index d276c9a10..65bafd4f5 100644
--- a/includes/ContentImport/Importers/PostThumbnail/Linking.php
+++ b/includes/ContentImport/Importers/PostThumbnail/Linking.php
@@ -63,15 +63,20 @@ public function import( array $data ) {
 		// In some instances, the folder sep. `/` might be duplicated, we de-duplicate it.
 		array_walk(
 			$source_upload_dir,
-			function ( &$entry ) {
-				$entry = str_replace( '//', '/', $entry );
+			function ( &$entry ): void {
+				if ( is_string( $entry ) ) {
+					$entry = str_replace( '//', '/', $entry );
+				}
 			}
 		);
+		$subdir = is_string( $source_upload_dir['subdir'] ) ? $source_upload_dir['subdir'] : '';
+		$path   = is_string( $source_upload_dir['path'] ) ? $source_upload_dir['path'] : '';
+
 		$source_uploads_dir         = untrailingslashit(
 			str_replace(
-				$source_upload_dir['subdir'],
+				$subdir,
 				'',
-				$source_upload_dir['path']
+				$path
 			)
 		);
 		$source_post_thumbnail_file = $source_uploads_dir . '/' . $source_post_thumbnail_meta['_wp_attached_file'];
@@ -91,7 +96,7 @@ function ( &$entry ) {
 		$found = get_posts(
 			array(
 				'post_type' => 'attachment',
-				'title'     => $attachment['post_title'],
+				'title'     => $attachment['post_title'] ?? '',
 			)
 		);
 		if ( isset( $found[0]->ID ) ) {
diff --git a/includes/ContentImport/Importers/PostThumbnailImporters.php b/includes/ContentImport/Importers/PostThumbnailImporters.php
index d1cb0716e..a658b42dd 100644
--- a/includes/ContentImport/Importers/PostThumbnailImporters.php
+++ b/includes/ContentImport/Importers/PostThumbnailImporters.php
@@ -9,7 +9,7 @@ class PostThumbnailImporters extends ImportersBaseFactory {
 	const TYPE = 'post-thumbnail';
 
 	/**
-	 * @var array<string, string>
+	 * @var array<string, class-string<Importer>>
 	 */
 	protected array $importers_map = array(
 		Linking::TYPE => Linking::class,
diff --git a/includes/ContentImport/Importers/Terms/ShallowDuplicating.php b/includes/ContentImport/Importers/Terms/ShallowDuplicating.php
index 49ac1479b..9120f3bec 100644
--- a/includes/ContentImport/Importers/Terms/ShallowDuplicating.php
+++ b/includes/ContentImport/Importers/Terms/ShallowDuplicating.php
@@ -53,7 +53,13 @@ public function import( array $data ) {
 
 		switch_to_blog( $source_blog_id );
 
-		$source_terms     = wp_get_post_terms( $source_post_id, get_taxonomies() );
+		$source_terms = wp_get_post_terms( $source_post_id, get_taxonomies() );
+		if ( is_wp_error( $source_terms ) ) {
+			restore_current_blog();
+
+			return $data;
+		}
+
 		$source_terms_ids = wp_list_pluck( $source_terms, 'term_id' );
 		$msls_terms       = array_combine(
 			$source_terms_ids,
@@ -62,7 +68,6 @@ public function import( array $data ) {
 
 		switch_to_blog( $this->import_coordinates->dest_blog_id );
 
-		/** @var \WP_Term $term */
 		foreach ( $source_terms as $term ) {
 			// is there a translation for the term in this blog?
 			$msls_term    = $msls_terms[ $term->term_id ];
@@ -72,7 +77,7 @@ public function import( array $data ) {
 				$dest_term_id = $this->create_local_term( $term, $msls_term, $dest_lang );
 			}
 
-			if ( false === $dest_term_id ) {
+			if ( ! is_int( $dest_term_id ) ) {
 				continue;
 			}
 
@@ -82,7 +87,7 @@ public function import( array $data ) {
 				// While we think the term translation exists it might not, let's create it.
 				$dest_term_id = $this->create_local_term( $term, $msls_term, $dest_lang );
 
-				if ( false === $dest_term_id ) {
+				if ( ! is_int( $dest_term_id ) ) {
 					continue;
 				}
 
diff --git a/includes/ContentImport/Importers/TermsImporters.php b/includes/ContentImport/Importers/TermsImporters.php
index 21b7d86d9..a06bd34c5 100644
--- a/includes/ContentImport/Importers/TermsImporters.php
+++ b/includes/ContentImport/Importers/TermsImporters.php
@@ -9,7 +9,7 @@ class TermsImporters extends ImportersBaseFactory {
 	const TYPE = 'terms';
 
 	/**
-	 * @var array<string, string>
+	 * @var array<string, class-string<Importer>>
 	 */
 	protected array $importers_map = array(
 		ShallowDuplicating::TYPE => ShallowDuplicating::class,
diff --git a/includes/ContentImport/MetaBox.php b/includes/ContentImport/MetaBox.php
index 9457cef69..577657d1d 100644
--- a/includes/ContentImport/MetaBox.php
+++ b/includes/ContentImport/MetaBox.php
@@ -23,7 +23,11 @@ class MetaBox extends MslsRegistryInstance {
 	 * Renders the content import metabox.
 	 */
 	public function render(): void {
-		$post            = get_post();
+		$post = get_post();
+		if ( ! $post instanceof \WP_Post ) {
+			return;
+		}
+
 		$mydata          = new MslsOptionsPost( $post->ID );
 		$languages       = MslsOptionsPost::instance()->get_available_languages();
 		$current         = MslsBlogCollection::get_blog_language( get_current_blog_id() );
@@ -185,6 +189,9 @@ protected function inline_thickbox_html( $output = true, array $data = array() )
 		<?php
 
 		$html = ob_get_clean();
+		if ( false === $html ) {
+			$html = '';
+		}
 
 		if ( $output ) {
 			echo wp_kses( $html, Component::get_allowed_html() );
diff --git a/includes/ContentImport/Relations.php b/includes/ContentImport/Relations.php
index b2b534845..a33adba24 100644
--- a/includes/ContentImport/Relations.php
+++ b/includes/ContentImport/Relations.php
@@ -21,7 +21,7 @@ class Relations {
 	public array $to_create = array();
 
 	/**
-	 * @var array<int, array<int, mixed>>
+	 * @var array<int, array{0: OptionsInterface, 1: int}>
 	 */
 	protected array $local_options = array();
 
@@ -93,7 +93,7 @@ protected function create_local_to_source(): void {
 			 * @param mixed $created If not `null` then the class will not create the local to source relation.
 			 * @param int $local_id
 			 * @param int $source_id
-			 * @param MslsOptions $source_option
+			 * @param OptionsInterface $source_option
 			 */
 			$created = apply_filters(
 				'msls_content_import_relation_local_to_source_create',
@@ -106,9 +106,15 @@ protected function create_local_to_source(): void {
 				continue;
 			}
 
+			if ( ! $source_option instanceof MslsOptions ) {
+				continue;
+			}
+
 			$option_class = get_class( $source_option );
-			$local_option = call_user_func( array( $option_class, 'create' ), $local_id );
-			$local_option->save( array( $this->import_coordinates->source_lang => $source_id ) );
+			$local_option = $option_class::create( $local_id );
+			if ( $local_option instanceof MslsOptions ) {
+				$local_option->save( array( $this->import_coordinates->source_lang => $source_id ) );
+			}
 		}
 	}
 
diff --git a/includes/MslsAdmin.php b/includes/MslsAdmin.php
index b21f30ef4..e5b31ae3c 100644
--- a/includes/MslsAdmin.php
+++ b/includes/MslsAdmin.php
@@ -11,6 +11,7 @@
 use lloc\Msls\Component\Input\Label;
 use lloc\Msls\Component\Input\Text;
 use lloc\Msls\Component\Input\Select;
+use WP_Post_Type;
 
 /**
  * Administration of the options
@@ -93,12 +94,12 @@ public function get_options_page_link(): string {
 	/**
 	 * You can use every method of the decorated object
 	 *
-	 * @param string $method
-	 * @param mixed  $args
+	 * @param string  $method
+	 * @param mixed[] $args
 	 *
 	 * @return mixed
 	 */
-	public function __call( string $method, $args ) {
+	public function __call( string $method, array $args ) {
 		$parts = explode( '_', $method, 2 );
 		if ( 2 === count( $parts ) && 'rewrite' === $parts[0] ) {
 			$this->render_rewrite( $parts[1] );
@@ -126,8 +127,13 @@ public function __call( string $method, $args ) {
 		);
 
 		if ( isset( $checkboxes[ $method ] ) ) {
+			$value = $this->options->$method;
+			if ( is_bool( $value ) ) {
+				$value = $value ? '1' : '';
+			}
+
 			$group = ( new Group() )
-				->add( new Checkbox( $method, $this->options->$method ) )
+				->add( new Checkbox( $method, $value ) )
 				->add( new Label( $method, $checkboxes[ $method ] ) );
 
 			echo $group->render(); // phpcs:ignore WordPress.Security.EscapeOutput
@@ -333,7 +339,11 @@ public function rewrites_section(): int {
 	 */
 	protected function add_settings_fields( array $map, string $section ): int {
 		foreach ( $map as $id => $title ) {
-			add_settings_field( $id, $title, array( $this, $id ), __CLASS__, $section, array( 'label_for' => $id ) );
+			$callback = array( $this, $id );
+			if ( ! is_callable( $callback ) ) {
+				continue;
+			}
+			add_settings_field( $id, $title, $callback, __CLASS__, $section, array( 'label_for' => $id ) );
 		}
 
 		/**
@@ -434,8 +444,8 @@ public function content_priority(): void {
 	 */
 	public function render_rewrite( $key ): void {
 		$pt_object = get_post_type_object( $key );
-		$rewrite   = $pt_object ? $pt_object->rewrite : array();
-		$value     = $rewrite['slug'] ?? '';
+		$rewrite   = $pt_object instanceof WP_Post_Type ? $pt_object->rewrite : null;
+		$value     = is_array( $rewrite ) ? ( $rewrite['slug'] ?? '' ) : '';
 
         // phpcs:ignore WordPress.Security.EscapeOutput
 		echo ( new Text( "rewrite_{$key}", $value, 30, true ) )->render();
diff --git a/includes/MslsBlogCollection.php b/includes/MslsBlogCollection.php
index 910fbc03c..fbfa5ba31 100644
--- a/includes/MslsBlogCollection.php
+++ b/includes/MslsBlogCollection.php
@@ -95,7 +95,10 @@ public function __construct() {
 				}
 			}
 
-			uasort( $this->objects, array( MslsBlog::class, $this->objects_order ) );
+			$compare = array( MslsBlog::class, $this->objects_order );
+			if ( is_callable( $compare ) ) {
+				uasort( $this->objects, $compare );
+			}
 		}
 	}
 
@@ -134,12 +137,11 @@ public function get_blogs_of_reference_user( MslsOptions $options ) {
 			$options->reference_user :
 			current( $this->get_users( 'ID', 1 ) );
 
-		$blogs = get_blogs_of_user( $reference_user );
-		foreach ( $blogs as $key => $blog ) {
-			$blogs[ $key ]->blog_id = $blog->userblog_id;
+		if ( ! is_int( $reference_user ) ) {
+			$reference_user = 0;
 		}
 
-		return $blogs;
+		return get_blogs_of_user( $reference_user );
 	}
 
 	/**
diff --git a/includes/MslsJson.php b/includes/MslsJson.php
index 7aabd10ff..a224dbf0e 100644
--- a/includes/MslsJson.php
+++ b/includes/MslsJson.php
@@ -11,7 +11,7 @@
 class MslsJson {
 
 	/**
-	 * @var array<int, array<string, string|int>>
+	 * @var array<int, array{value: int, label: string}>
 	 */
 	protected array $arr = array();
 
@@ -35,8 +35,8 @@ public function add( $value, $label ) {
 	/**
 	 * Compare the item with the key "label" of the array $a and the array $b
 	 *
-	 * @param array<string, string> $a
-	 * @param array<string, string> $b
+	 * @param array{value: int, label: string} $a
+	 * @param array{value: int, label: string} $b
 	 *
 	 * @return int
 	 */
@@ -47,7 +47,7 @@ public static function compare( array $a, array $b ): int {
 	/**
 	 * Get the array container sorted by label
 	 *
-	 * @return array<int, array<string, string|int>>
+	 * @return array<int, array{value: int, label: string}>
 	 */
 	public function get(): array {
 		$arr = $this->arr;
diff --git a/includes/MslsLink.php b/includes/MslsLink.php
index 6d25860d2..da28f8838 100644
--- a/includes/MslsLink.php
+++ b/includes/MslsLink.php
@@ -19,7 +19,7 @@ class MslsLink extends MslsGetSet implements LinkInterface {
 	/**
 	 * Gets all link types as an array with "id => name"-items
 	 *
-	 * @return string[]
+	 * @return array<int, class-string<LinkInterface>>
 	 */
 	public static function get_types() {
 		return array(
@@ -42,13 +42,13 @@ public static function get_description(): string {
 	/**
 	 * Gets an array with all link descriptions
 	 *
-	 * @return array<string, string>
+	 * @return array<int, string>
 	 */
 	public static function get_types_description(): array {
 		$types = array();
 
 		foreach ( self::get_types() as $key => $class ) {
-			$types[ $key ] = call_user_func( array( $class, 'get_description' ) );
+			$types[ $key ] = $class::get_description();
 		}
 
 		return $types;
@@ -70,11 +70,10 @@ public static function create( ?int $display ): LinkInterface {
 		$obj = new $types[ $display ]();
 
 		if ( has_filter( 'msls_link_create' ) ) {
-			/**
-			 * @param LinkInterface $obj
-			 * @param int $display
-			 */
-			$obj = apply_filters( 'msls_link_create', $obj, $display );
+			$filtered = apply_filters( 'msls_link_create', $obj, $display );
+			if ( $filtered instanceof LinkInterface ) {
+				$obj = $filtered;
+			}
 		}
 
 		return $obj;
diff --git a/includes/MslsMain.php b/includes/MslsMain.php
index e8d552ecf..8929e3e80 100644
--- a/includes/MslsMain.php
+++ b/includes/MslsMain.php
@@ -125,8 +125,8 @@ public function delete( $object_id ): void {
 	/**
 	 * Save
 	 *
-	 * @param int    $object_id
-	 * @param string $class_name
+	 * @param int                       $object_id
+	 * @param class-string<MslsOptions> $class_name
 	 *
 	 * @codeCoverageIgnore
 	 */
@@ -145,13 +145,14 @@ protected function save( $object_id, $class_name ): void {
 			return;
 		}
 
-		if ( ! $this->collection->has_current_blog() ) {
+		$current_blog = $this->collection->get_current_blog();
+		if ( ! $current_blog instanceof MslsBlog ) {
 			$this->debugger( 'BlogCollection returns false when calling has_current_blog.' );
 
 			return;
 		}
 
-		$language = $this->collection->get_current_blog()->get_language();
+		$language = $current_blog->get_language();
 		$msla     = new MslsLanguageArray( $this->get_input_array( $object_id ) );
 		$options  = new $class_name( $object_id );
 		$temp     = $options->get_arr();
diff --git a/includes/MslsMetaBox.php b/includes/MslsMetaBox.php
index 8cf607a04..d25d7e200 100644
--- a/includes/MslsMetaBox.php
+++ b/includes/MslsMetaBox.php
@@ -89,7 +89,7 @@ public static function suggest(): void {
 		);
 
 		// phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped
-		wp_die( wp_json_encode( $results ) );
+		wp_die( wp_json_encode( $results ) ?: '' );
 	}
 
 	/**
@@ -109,14 +109,19 @@ public static function get_suggested_fields( MslsJson $json, array $args ): Msls
 		$args = (array) apply_filters( 'msls_meta_box_suggest_args', $args );
 
 		foreach ( get_posts( $args ) as $post ) {
+			if ( ! $post instanceof \WP_Post ) {
+				continue;
+			}
+
 			/**
 			 * Manipulates the WP_Post object before using it
 			 *
-			 * @param WP_Post $post
-			 *
 			 * @since 0.9.9
 			 */
-			$post = apply_filters( 'msls_meta_box_suggest_post', $post );
+			$filtered = apply_filters( 'msls_meta_box_suggest_post', $post );
+			if ( $filtered instanceof \WP_Post ) {
+				$post = $filtered;
+			}
 
 			$json->add( $post->ID, get_the_title( $post ) );
 		}
@@ -181,7 +186,11 @@ public function render_select(): void {
 		if ( $blogs ) {
 			global $post;
 
-			$type            = get_post_type( $post->ID );
+			$type = get_post_type( $post->ID );
+			if ( false === $type ) {
+				return;
+			}
+
 			$mydata          = new MslsOptionsPost( $post->ID );
 			$origin_language = MslsBlogCollection::get_blog_language();
 			$is_saved        = 'auto-draft' !== get_post_status( $post );
@@ -321,7 +330,11 @@ public function render_input(): void {
 		if ( $blogs ) {
 			global $post;
 
-			$post_type       = get_post_type( $post->ID );
+			$post_type = get_post_type( $post->ID );
+			if ( false === $post_type ) {
+				return;
+			}
+
 			$my_data         = new MslsOptionsPost( $post->ID );
 			$origin_language = MslsBlogCollection::get_blog_language();
 			$is_saved        = 'auto-draft' !== get_post_status( $post );
diff --git a/includes/MslsOptions.php b/includes/MslsOptions.php
index 286b0956f..82f2f0011 100644
--- a/includes/MslsOptions.php
+++ b/includes/MslsOptions.php
@@ -101,12 +101,12 @@ public static function create( $id = 0 ) {
 		} elseif ( self::is_tax_page() ) {
 			$options = MslsOptionsTax::create();
 		} elseif ( self::is_query_page() ) {
-			$options = MslsOptionsQuery::create();
+			$options = MslsOptionsQuery::create() ?? new MslsOptions();
 		} else {
 			$options = new MslsOptionsPost( get_queried_object_id() );
 		}
 
-		add_filter( self::MSLS_GET_POSTLINK_HOOK, array( $options, 'check_for_blog_slug' ), 10, 2 );
+		add_filter( self::MSLS_GET_POSTLINK_HOOK, array( self::class, 'check_for_blog_slug' ), 10, 2 );
 
 		return $options;
 	}
diff --git a/includes/MslsPostTag.php b/includes/MslsPostTag.php
index d5a156862..d77d1212b 100644
--- a/includes/MslsPostTag.php
+++ b/includes/MslsPostTag.php
@@ -55,8 +55,12 @@ public static function suggest(): void {
 			 *
 			 * @since 0.9.9
 			 */
-			$args = (array) apply_filters( 'msls_post_tag_suggest_args', $args );
-			foreach ( get_terms( $args ) as $term ) {
+			$args  = (array) apply_filters( 'msls_post_tag_suggest_args', $args );
+			$terms = get_terms( $args );
+			if ( ! is_array( $terms ) ) {
+				$terms = array();
+			}
+			foreach ( $terms as $term ) {
 				/**
 				 * Manipulates the term object before using it
 				 *
diff --git a/includes/MslsShortCode.php b/includes/MslsShortCode.php
index 4e5cf2a1a..6e21db094 100644
--- a/includes/MslsShortCode.php
+++ b/includes/MslsShortCode.php
@@ -12,9 +12,13 @@ public static function init(): void {
 	/**
 	 * Renders output using the widget's output
 	 *
-	 * @return string|false
+	 * @param array<string>|string $atts
+	 * @param string|null          $content
+	 * @param string               $tag
+	 *
+	 * @return string
 	 */
-	public static function render_widget() {
+	public static function render_widget( $atts = array(), ?string $content = null, string $tag = '' ): string {
 		if ( msls_options()->is_excluded() ) {
 			return '';
 		}
@@ -23,6 +27,6 @@ public static function render_widget() {
 		the_widget( MslsWidget::class );
 		$output = ob_get_clean();
 
-		return $output;
+		return false === $output ? '' : $output;
 	}
 }
diff --git a/includes/MslsSqlCacher.php b/includes/MslsSqlCacher.php
index 0e10bfecd..34d9acabb 100644
--- a/includes/MslsSqlCacher.php
+++ b/includes/MslsSqlCacher.php
@@ -94,15 +94,30 @@ public function __get( string $name ) {
 	 */
 	public function __call( string $method, array $args ) {
 		if ( 'get_' !== substr( $method, 0, 4 ) ) {
-			return call_user_func_array( array( $this->db, $method ), $args );
+			return $this->invoke( $method, $args );
 		}
 
 		$result = wp_cache_get( $this->cache_key, self::CACHE_GROUP );
 		if ( false === $result ) {
-			$result = call_user_func_array( array( $this->db, $method ), $args );
+			$result = $this->invoke( $method, $args );
 			wp_cache_set( $this->cache_key, $result, self::CACHE_GROUP, $this->expire );
 		}
 
 		return $result;
 	}
+
+	/**
+	 * @param string            $method
+	 * @param array<int|string> $args
+	 *
+	 * @return mixed
+	 */
+	protected function invoke( string $method, array $args ) {
+		$callback = array( $this->db, $method );
+		if ( ! is_callable( $callback ) ) {
+			return null;
+		}
+
+		return $callback( ...$args );
+	}
 }
diff --git a/includes/MslsTranslationPickerTable.php b/includes/MslsTranslationPickerTable.php
index b8bf1c861..f389315cb 100644
--- a/includes/MslsTranslationPickerTable.php
+++ b/includes/MslsTranslationPickerTable.php
@@ -191,6 +191,10 @@ public function prepare_items(): void {
 		$taxonomies = array_keys( $this->get_admin_column_taxonomies() );
 
 		foreach ( $query->posts as $post ) {
+			if ( ! $post instanceof \WP_Post ) {
+				continue;
+			}
+
 			$terms_by_tax = array();
 			foreach ( $taxonomies as $tax_name ) {
 				$terms                     = get_the_terms( $post->ID, $tax_name );
diff --git a/tests/phpunit/ContentImport/TestContentImporter.php b/tests/phpunit/ContentImport/TestContentImporter.php
index a94d24304..a80879191 100644
--- a/tests/phpunit/ContentImport/TestContentImporter.php
+++ b/tests/phpunit/ContentImport/TestContentImporter.php
@@ -43,7 +43,7 @@ public function test_handle_import(): void {
 	public function test_parse_sources_no_post(): void {
 		$test = $this->ContentImporterFactory();
 
-		$this->assertFalse( $test->parse_sources() );
+		$this->assertNull( $test->parse_sources() );
 	}
 
 	public function test_handle_false(): void {
diff --git a/tests/phpunit/TestMslsAdminIcon.php b/tests/phpunit/TestMslsAdminIcon.php
index 00b0a8211..77e4d5935 100644
--- a/tests/phpunit/TestMslsAdminIcon.php
+++ b/tests/phpunit/TestMslsAdminIcon.php
@@ -152,7 +152,7 @@ public function test_get_img_post_page(): void {
 	}
 
 	public function test_set_id_with_null_constructor(): void {
-		Functions\expect( 'add_query_arg' )->once();
+		Functions\expect( 'add_query_arg' )->once()->andReturn( 'post-new.php' );
 
 		$obj = new MslsAdminIcon( null );