From ce147ee72c14ae8909698daf4c2ea05ce9d38839 Mon Sep 17 00:00:00 2001
From: box-sdk-build <sdk-build@box.com>
Date: Wed, 22 Apr 2026 08:20:24 -0700
Subject: [PATCH 1/2] chore: Update `.codegen.json` with commit hash of
 `codegen` and `openapi` spec [skip ci]

---
 .codegen.json | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.codegen.json b/.codegen.json
index 7d9d03d08..15f71d59b 100644
--- a/.codegen.json
+++ b/.codegen.json
@@ -1 +1 @@
-{ "engineHash": "450fb53", "specHash": "d0976fc", "version": "10.9.0" }
+{ "engineHash": "ae9c271", "specHash": "d0976fc", "version": "10.9.0" }

From 2d2a4a6305029a2d03853eec72d8bc94dbe36aa1 Mon Sep 17 00:00:00 2001
From: box-sdk-build <sdk-build@box.com>
Date: Fri, 24 Apr 2026 09:50:49 -0700
Subject: [PATCH 2/2] fix: Fix java oneOf serialization (box/box-codegen#942)

---
 .codegen.json                                 |  2 +-
 .../internal/NullablePropertyFilter.java      |  5 +--
 .../com/box/sdkgen/internal/OneOfEight.java   | 24 +++++++++++++-
 .../com/box/sdkgen/internal/OneOfEleven.java  | 30 +++++++++++++++++-
 .../com/box/sdkgen/internal/OneOfFive.java    | 13 +++++++-
 .../com/box/sdkgen/internal/OneOfFour.java    | 12 ++++++-
 .../com/box/sdkgen/internal/OneOfNine.java    | 26 +++++++++++++++-
 .../com/box/sdkgen/internal/OneOfOne.java     |  9 +++++-
 .../com/box/sdkgen/internal/OneOfSeven.java   | 22 ++++++++++++-
 .../com/box/sdkgen/internal/OneOfSix.java     | 19 +++++++++++-
 .../com/box/sdkgen/internal/OneOfTen.java     | 28 ++++++++++++++++-
 .../com/box/sdkgen/internal/OneOfThree.java   | 11 ++++++-
 .../com/box/sdkgen/internal/OneOfTwelve.java  | 31 ++++++++++++++++++-
 .../com/box/sdkgen/internal/OneOfTwo.java     | 10 +++++-
 .../com/box/sdkgen/internal/OneOfUnion.java   |  7 +++++
 15 files changed, 234 insertions(+), 15 deletions(-)
 create mode 100644 src/main/java/com/box/sdkgen/internal/OneOfUnion.java

diff --git a/.codegen.json b/.codegen.json
index 15f71d59b..d0b124df6 100644
--- a/.codegen.json
+++ b/.codegen.json
@@ -1 +1 @@
-{ "engineHash": "ae9c271", "specHash": "d0976fc", "version": "10.9.0" }
+{ "engineHash": "a82031b", "specHash": "d0976fc", "version": "10.9.0" }
diff --git a/src/main/java/com/box/sdkgen/internal/NullablePropertyFilter.java b/src/main/java/com/box/sdkgen/internal/NullablePropertyFilter.java
index 5353ba292..40503a0bd 100644
--- a/src/main/java/com/box/sdkgen/internal/NullablePropertyFilter.java
+++ b/src/main/java/com/box/sdkgen/internal/NullablePropertyFilter.java
@@ -30,8 +30,9 @@ public void serializeAsField(
       return;
     }
 
-    // For non-nullable fields, serialize only if the value is not null
-    if (value != null) {
+    boolean isOneOfWithNoNonNullValue =
+        value instanceof OneOfUnion && !((OneOfUnion) value).hasAnyNonNullValue();
+    if (value != null && !isOneOfWithNoNonNullValue) {
       writer.serializeAsField(pojo, jgen, provider);
     }
   }
diff --git a/src/main/java/com/box/sdkgen/internal/OneOfEight.java b/src/main/java/com/box/sdkgen/internal/OneOfEight.java
index a20e86ec1..c7169965b 100644
--- a/src/main/java/com/box/sdkgen/internal/OneOfEight.java
+++ b/src/main/java/com/box/sdkgen/internal/OneOfEight.java
@@ -7,7 +7,8 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import java.io.IOException;
 
-public class OneOfEight<T0, T1, T2, T3, T4, T5, T6, T7> extends SerializableObject {
+public class OneOfEight<T0, T1, T2, T3, T4, T5, T6, T7> extends SerializableObject
+    implements OneOfUnion {
   protected static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
   protected T0 value0;
   protected T1 value1;
@@ -30,6 +31,18 @@ public OneOfEight(
     this.value7 = value7;
   }
 
+  @Override
+  public boolean hasAnyNonNullValue() {
+    return value0 != null
+        || value1 != null
+        || value2 != null
+        || value3 != null
+        || value4 != null
+        || value5 != null
+        || value6 != null
+        || value7 != null;
+  }
+
   public static class OneOfEightSerializer
       extends JsonSerializer<OneOfEight<?, ?, ?, ?, ?, ?, ?, ?>> {
 
@@ -45,28 +58,37 @@ public void serialize(
         throws IOException {
       if (itemEntryField.value0 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value0);
+        return;
       }
       if (itemEntryField.value1 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value1);
+        return;
       }
       if (itemEntryField.value2 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value2);
+        return;
       }
       if (itemEntryField.value3 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value3);
+        return;
       }
       if (itemEntryField.value4 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value4);
+        return;
       }
       if (itemEntryField.value5 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value5);
+        return;
       }
       if (itemEntryField.value6 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value6);
+        return;
       }
       if (itemEntryField.value7 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value7);
+        return;
       }
+      gen.writeNull();
     }
   }
 }
diff --git a/src/main/java/com/box/sdkgen/internal/OneOfEleven.java b/src/main/java/com/box/sdkgen/internal/OneOfEleven.java
index 5b5485d24..8c7ecb077 100644
--- a/src/main/java/com/box/sdkgen/internal/OneOfEleven.java
+++ b/src/main/java/com/box/sdkgen/internal/OneOfEleven.java
@@ -7,7 +7,8 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import java.io.IOException;
 
-public class OneOfEleven<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10> extends SerializableObject {
+public class OneOfEleven<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10> extends SerializableObject
+    implements OneOfUnion {
   protected static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
   protected T0 value0;
   protected T1 value1;
@@ -46,6 +47,21 @@ public OneOfEleven(
     this.value10 = value10;
   }
 
+  @Override
+  public boolean hasAnyNonNullValue() {
+    return value0 != null
+        || value1 != null
+        || value2 != null
+        || value3 != null
+        || value4 != null
+        || value5 != null
+        || value6 != null
+        || value7 != null
+        || value8 != null
+        || value9 != null
+        || value10 != null;
+  }
+
   public static class OneOfElevenSerializer
       extends JsonSerializer<OneOfEleven<?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?>> {
 
@@ -61,37 +77,49 @@ public void serialize(
         throws IOException {
       if (itemEntryField.value0 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value0);
+        return;
       }
       if (itemEntryField.value1 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value1);
+        return;
       }
       if (itemEntryField.value2 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value2);
+        return;
       }
       if (itemEntryField.value3 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value3);
+        return;
       }
       if (itemEntryField.value4 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value4);
+        return;
       }
       if (itemEntryField.value5 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value5);
+        return;
       }
       if (itemEntryField.value6 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value6);
+        return;
       }
       if (itemEntryField.value7 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value7);
+        return;
       }
       if (itemEntryField.value8 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value8);
+        return;
       }
       if (itemEntryField.value9 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value9);
+        return;
       }
       if (itemEntryField.value10 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value10);
+        return;
       }
+      gen.writeNull();
     }
   }
 }
diff --git a/src/main/java/com/box/sdkgen/internal/OneOfFive.java b/src/main/java/com/box/sdkgen/internal/OneOfFive.java
index bc8a13927..0f762ae97 100644
--- a/src/main/java/com/box/sdkgen/internal/OneOfFive.java
+++ b/src/main/java/com/box/sdkgen/internal/OneOfFive.java
@@ -7,7 +7,7 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import java.io.IOException;
 
-public class OneOfFive<T0, T1, T2, T3, T4> extends SerializableObject {
+public class OneOfFive<T0, T1, T2, T3, T4> extends SerializableObject implements OneOfUnion {
   protected static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
   protected T0 value0;
   protected T1 value1;
@@ -23,6 +23,11 @@ public OneOfFive(T0 value0, T1 value1, T2 value2, T3 value3, T4 value4) {
     this.value4 = value4;
   }
 
+  @Override
+  public boolean hasAnyNonNullValue() {
+    return value0 != null || value1 != null || value2 != null || value3 != null || value4 != null;
+  }
+
   public static class OneOfFiveSerializer extends JsonSerializer<OneOfFive<?, ?, ?, ?, ?>> {
 
     public OneOfFiveSerializer() {
@@ -35,19 +40,25 @@ public void serialize(
         throws IOException {
       if (itemEntryField.value0 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value0);
+        return;
       }
       if (itemEntryField.value1 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value1);
+        return;
       }
       if (itemEntryField.value2 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value2);
+        return;
       }
       if (itemEntryField.value3 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value3);
+        return;
       }
       if (itemEntryField.value4 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value4);
+        return;
       }
+      gen.writeNull();
     }
   }
 }
diff --git a/src/main/java/com/box/sdkgen/internal/OneOfFour.java b/src/main/java/com/box/sdkgen/internal/OneOfFour.java
index ee86354c8..32383289a 100644
--- a/src/main/java/com/box/sdkgen/internal/OneOfFour.java
+++ b/src/main/java/com/box/sdkgen/internal/OneOfFour.java
@@ -7,7 +7,7 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import java.io.IOException;
 
-public class OneOfFour<T0, T1, T2, T3> extends SerializableObject {
+public class OneOfFour<T0, T1, T2, T3> extends SerializableObject implements OneOfUnion {
   protected static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
   protected T0 value0;
   protected T1 value1;
@@ -21,6 +21,11 @@ public OneOfFour(T0 value0, T1 value1, T2 value2, T3 value3) {
     this.value3 = value3;
   }
 
+  @Override
+  public boolean hasAnyNonNullValue() {
+    return value0 != null || value1 != null || value2 != null || value3 != null;
+  }
+
   public static class OneOfFourSerializer extends JsonSerializer<OneOfFour<?, ?, ?, ?>> {
 
     public OneOfFourSerializer() {
@@ -33,16 +38,21 @@ public void serialize(
         throws IOException {
       if (itemEntryField.value0 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value0);
+        return;
       }
       if (itemEntryField.value1 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value1);
+        return;
       }
       if (itemEntryField.value2 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value2);
+        return;
       }
       if (itemEntryField.value3 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value3);
+        return;
       }
+      gen.writeNull();
     }
   }
 }
diff --git a/src/main/java/com/box/sdkgen/internal/OneOfNine.java b/src/main/java/com/box/sdkgen/internal/OneOfNine.java
index 6da57f0bc..42bc824ca 100644
--- a/src/main/java/com/box/sdkgen/internal/OneOfNine.java
+++ b/src/main/java/com/box/sdkgen/internal/OneOfNine.java
@@ -7,7 +7,8 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import java.io.IOException;
 
-public class OneOfNine<T0, T1, T2, T3, T4, T5, T6, T7, T8> extends SerializableObject {
+public class OneOfNine<T0, T1, T2, T3, T4, T5, T6, T7, T8> extends SerializableObject
+    implements OneOfUnion {
   protected static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
   protected T0 value0;
   protected T1 value1;
@@ -40,6 +41,19 @@ public OneOfNine(
     this.value8 = value8;
   }
 
+  @Override
+  public boolean hasAnyNonNullValue() {
+    return value0 != null
+        || value1 != null
+        || value2 != null
+        || value3 != null
+        || value4 != null
+        || value5 != null
+        || value6 != null
+        || value7 != null
+        || value8 != null;
+  }
+
   public static class OneOfNineSerializer
       extends JsonSerializer<OneOfNine<?, ?, ?, ?, ?, ?, ?, ?, ?>> {
 
@@ -55,31 +69,41 @@ public void serialize(
         throws IOException {
       if (itemEntryField.value0 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value0);
+        return;
       }
       if (itemEntryField.value1 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value1);
+        return;
       }
       if (itemEntryField.value2 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value2);
+        return;
       }
       if (itemEntryField.value3 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value3);
+        return;
       }
       if (itemEntryField.value4 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value4);
+        return;
       }
       if (itemEntryField.value5 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value5);
+        return;
       }
       if (itemEntryField.value6 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value6);
+        return;
       }
       if (itemEntryField.value7 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value7);
+        return;
       }
       if (itemEntryField.value8 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value8);
+        return;
       }
+      gen.writeNull();
     }
   }
 }
diff --git a/src/main/java/com/box/sdkgen/internal/OneOfOne.java b/src/main/java/com/box/sdkgen/internal/OneOfOne.java
index 67b073885..cf9761160 100644
--- a/src/main/java/com/box/sdkgen/internal/OneOfOne.java
+++ b/src/main/java/com/box/sdkgen/internal/OneOfOne.java
@@ -7,7 +7,7 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import java.io.IOException;
 
-public class OneOfOne<T0> extends SerializableObject {
+public class OneOfOne<T0> extends SerializableObject implements OneOfUnion {
   protected static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
   protected T0 value0;
 
@@ -15,6 +15,11 @@ public OneOfOne(T0 value0) {
     this.value0 = value0;
   }
 
+  @Override
+  public boolean hasAnyNonNullValue() {
+    return value0 != null;
+  }
+
   public static class OneOfOneSerializer extends JsonSerializer<OneOfOne<?>> {
 
     public OneOfOneSerializer() {
@@ -27,7 +32,9 @@ public void serialize(
         throws IOException {
       if (itemEntryField.value0 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value0);
+        return;
       }
+      gen.writeNull();
     }
   }
 }
diff --git a/src/main/java/com/box/sdkgen/internal/OneOfSeven.java b/src/main/java/com/box/sdkgen/internal/OneOfSeven.java
index e07226eba..7687bb956 100644
--- a/src/main/java/com/box/sdkgen/internal/OneOfSeven.java
+++ b/src/main/java/com/box/sdkgen/internal/OneOfSeven.java
@@ -7,7 +7,8 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import java.io.IOException;
 
-public class OneOfSeven<T0, T1, T2, T3, T4, T5, T6> extends SerializableObject {
+public class OneOfSeven<T0, T1, T2, T3, T4, T5, T6> extends SerializableObject
+    implements OneOfUnion {
   protected static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
   protected T0 value0;
   protected T1 value1;
@@ -27,6 +28,17 @@ public OneOfSeven(T0 value0, T1 value1, T2 value2, T3 value3, T4 value4, T5 valu
     this.value6 = value6;
   }
 
+  @Override
+  public boolean hasAnyNonNullValue() {
+    return value0 != null
+        || value1 != null
+        || value2 != null
+        || value3 != null
+        || value4 != null
+        || value5 != null
+        || value6 != null;
+  }
+
   public static class OneOfSevenSerializer extends JsonSerializer<OneOfSeven<?, ?, ?, ?, ?, ?, ?>> {
 
     public OneOfSevenSerializer() {
@@ -41,25 +53,33 @@ public void serialize(
         throws IOException {
       if (itemEntryField.value0 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value0);
+        return;
       }
       if (itemEntryField.value1 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value1);
+        return;
       }
       if (itemEntryField.value2 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value2);
+        return;
       }
       if (itemEntryField.value3 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value3);
+        return;
       }
       if (itemEntryField.value4 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value4);
+        return;
       }
       if (itemEntryField.value5 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value5);
+        return;
       }
       if (itemEntryField.value6 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value6);
+        return;
       }
+      gen.writeNull();
     }
   }
 }
diff --git a/src/main/java/com/box/sdkgen/internal/OneOfSix.java b/src/main/java/com/box/sdkgen/internal/OneOfSix.java
index d3ed9a566..c473544bd 100644
--- a/src/main/java/com/box/sdkgen/internal/OneOfSix.java
+++ b/src/main/java/com/box/sdkgen/internal/OneOfSix.java
@@ -7,7 +7,7 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import java.io.IOException;
 
-public class OneOfSix<T0, T1, T2, T3, T4, T5> extends SerializableObject {
+public class OneOfSix<T0, T1, T2, T3, T4, T5> extends SerializableObject implements OneOfUnion {
   protected static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
   protected T0 value0;
   protected T1 value1;
@@ -25,6 +25,16 @@ public OneOfSix(T0 value0, T1 value1, T2 value2, T3 value3, T4 value4, T5 value5
     this.value5 = value5;
   }
 
+  @Override
+  public boolean hasAnyNonNullValue() {
+    return value0 != null
+        || value1 != null
+        || value2 != null
+        || value3 != null
+        || value4 != null
+        || value5 != null;
+  }
+
   public static class OneOfSixSerializer extends JsonSerializer<OneOfSix<?, ?, ?, ?, ?, ?>> {
 
     public OneOfSixSerializer() {
@@ -37,22 +47,29 @@ public void serialize(
         throws IOException {
       if (itemEntryField.value0 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value0);
+        return;
       }
       if (itemEntryField.value1 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value1);
+        return;
       }
       if (itemEntryField.value2 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value2);
+        return;
       }
       if (itemEntryField.value3 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value3);
+        return;
       }
       if (itemEntryField.value4 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value4);
+        return;
       }
       if (itemEntryField.value5 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value5);
+        return;
       }
+      gen.writeNull();
     }
   }
 }
diff --git a/src/main/java/com/box/sdkgen/internal/OneOfTen.java b/src/main/java/com/box/sdkgen/internal/OneOfTen.java
index 6af089e2a..2738670f7 100644
--- a/src/main/java/com/box/sdkgen/internal/OneOfTen.java
+++ b/src/main/java/com/box/sdkgen/internal/OneOfTen.java
@@ -7,7 +7,8 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import java.io.IOException;
 
-public class OneOfTen<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9> extends SerializableObject {
+public class OneOfTen<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9> extends SerializableObject
+    implements OneOfUnion {
   protected static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
   protected T0 value0;
   protected T1 value1;
@@ -43,6 +44,20 @@ public OneOfTen(
     this.value9 = value9;
   }
 
+  @Override
+  public boolean hasAnyNonNullValue() {
+    return value0 != null
+        || value1 != null
+        || value2 != null
+        || value3 != null
+        || value4 != null
+        || value5 != null
+        || value6 != null
+        || value7 != null
+        || value8 != null
+        || value9 != null;
+  }
+
   public static class OneOfTenSerializer
       extends JsonSerializer<OneOfTen<?, ?, ?, ?, ?, ?, ?, ?, ?, ?>> {
 
@@ -58,34 +73,45 @@ public void serialize(
         throws IOException {
       if (itemEntryField.value0 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value0);
+        return;
       }
       if (itemEntryField.value1 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value1);
+        return;
       }
       if (itemEntryField.value2 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value2);
+        return;
       }
       if (itemEntryField.value3 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value3);
+        return;
       }
       if (itemEntryField.value4 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value4);
+        return;
       }
       if (itemEntryField.value5 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value5);
+        return;
       }
       if (itemEntryField.value6 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value6);
+        return;
       }
       if (itemEntryField.value7 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value7);
+        return;
       }
       if (itemEntryField.value8 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value8);
+        return;
       }
       if (itemEntryField.value9 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value9);
+        return;
       }
+      gen.writeNull();
     }
   }
 }
diff --git a/src/main/java/com/box/sdkgen/internal/OneOfThree.java b/src/main/java/com/box/sdkgen/internal/OneOfThree.java
index 9319155d8..5f9e900af 100644
--- a/src/main/java/com/box/sdkgen/internal/OneOfThree.java
+++ b/src/main/java/com/box/sdkgen/internal/OneOfThree.java
@@ -7,7 +7,7 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import java.io.IOException;
 
-public class OneOfThree<T0, T1, T2> extends SerializableObject {
+public class OneOfThree<T0, T1, T2> extends SerializableObject implements OneOfUnion {
   protected static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
   protected T0 value0;
   protected T1 value1;
@@ -19,6 +19,11 @@ public OneOfThree(T0 value0, T1 value1, T2 value2) {
     this.value2 = value2;
   }
 
+  @Override
+  public boolean hasAnyNonNullValue() {
+    return value0 != null || value1 != null || value2 != null;
+  }
+
   public static class OneOfThreeSerializer extends JsonSerializer<OneOfThree<?, ?, ?>> {
 
     public OneOfThreeSerializer() {
@@ -31,13 +36,17 @@ public void serialize(
         throws IOException {
       if (itemEntryField.value0 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value0);
+        return;
       }
       if (itemEntryField.value1 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value1);
+        return;
       }
       if (itemEntryField.value2 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value2);
+        return;
       }
+      gen.writeNull();
     }
   }
 }
diff --git a/src/main/java/com/box/sdkgen/internal/OneOfTwelve.java b/src/main/java/com/box/sdkgen/internal/OneOfTwelve.java
index a411e9cc6..13de4e1a7 100644
--- a/src/main/java/com/box/sdkgen/internal/OneOfTwelve.java
+++ b/src/main/java/com/box/sdkgen/internal/OneOfTwelve.java
@@ -8,7 +8,7 @@
 import java.io.IOException;
 
 public class OneOfTwelve<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11>
-    extends SerializableObject {
+    extends SerializableObject implements OneOfUnion {
   protected static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
   protected T0 value0;
   protected T1 value1;
@@ -50,6 +50,22 @@ public OneOfTwelve(
     this.value11 = value11;
   }
 
+  @Override
+  public boolean hasAnyNonNullValue() {
+    return value0 != null
+        || value1 != null
+        || value2 != null
+        || value3 != null
+        || value4 != null
+        || value5 != null
+        || value6 != null
+        || value7 != null
+        || value8 != null
+        || value9 != null
+        || value10 != null
+        || value11 != null;
+  }
+
   public static class OneOfTwelveSerializer
       extends JsonSerializer<OneOfTwelve<?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?>> {
 
@@ -65,40 +81,53 @@ public void serialize(
         throws IOException {
       if (itemEntryField.value0 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value0);
+        return;
       }
       if (itemEntryField.value1 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value1);
+        return;
       }
       if (itemEntryField.value2 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value2);
+        return;
       }
       if (itemEntryField.value3 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value3);
+        return;
       }
       if (itemEntryField.value4 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value4);
+        return;
       }
       if (itemEntryField.value5 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value5);
+        return;
       }
       if (itemEntryField.value6 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value6);
+        return;
       }
       if (itemEntryField.value7 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value7);
+        return;
       }
       if (itemEntryField.value8 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value8);
+        return;
       }
       if (itemEntryField.value9 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value9);
+        return;
       }
       if (itemEntryField.value10 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value10);
+        return;
       }
       if (itemEntryField.value11 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value11);
+        return;
       }
+      gen.writeNull();
     }
   }
 }
diff --git a/src/main/java/com/box/sdkgen/internal/OneOfTwo.java b/src/main/java/com/box/sdkgen/internal/OneOfTwo.java
index 6058a4f59..94d226185 100644
--- a/src/main/java/com/box/sdkgen/internal/OneOfTwo.java
+++ b/src/main/java/com/box/sdkgen/internal/OneOfTwo.java
@@ -7,7 +7,7 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import java.io.IOException;
 
-public class OneOfTwo<T0, T1> extends SerializableObject {
+public class OneOfTwo<T0, T1> extends SerializableObject implements OneOfUnion {
   protected static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
   protected T0 value0;
   protected T1 value1;
@@ -17,6 +17,11 @@ public OneOfTwo(T0 value0, T1 value1) {
     this.value1 = value1;
   }
 
+  @Override
+  public boolean hasAnyNonNullValue() {
+    return value0 != null || value1 != null;
+  }
+
   public static class OneOfTwoSerializer extends JsonSerializer<OneOfTwo<?, ?>> {
 
     public OneOfTwoSerializer() {
@@ -29,10 +34,13 @@ public void serialize(
         throws IOException {
       if (itemEntryField.value0 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value0);
+        return;
       }
       if (itemEntryField.value1 != null) {
         JsonManager.WRITER.writeValue(gen, itemEntryField.value1);
+        return;
       }
+      gen.writeNull();
     }
   }
 }
diff --git a/src/main/java/com/box/sdkgen/internal/OneOfUnion.java b/src/main/java/com/box/sdkgen/internal/OneOfUnion.java
new file mode 100644
index 000000000..59c4dd4b0
--- /dev/null
+++ b/src/main/java/com/box/sdkgen/internal/OneOfUnion.java
@@ -0,0 +1,7 @@
+package com.box.sdkgen.internal;
+
+public interface OneOfUnion {
+
+  /** @return {@code true} if at least one branch holds a non-null value */
+  boolean hasAnyNonNullValue();
+}