refactor: Simplify health-probe null handling

Author: thced

src/main/java/com/retailsvc/http/Handlers.java

@@ -89,11 +89,7 @@ public static HttpHandler healthHandler(Supplier<HealthOutcome> probe) {
           try (exchange) {
             HealthOutcome outcome;
             try {
-              HealthOutcome result = probe.get();
-              if (result == null) {
-                throw new IllegalStateException("Health probe returned null");
-              }
-              outcome = result;
+              outcome = Objects.requireNonNull(probe.get(), "Health probe returned null");
             } catch (RuntimeException e) {
               LOG.warn("Health probe failed", e);
               outcome = new HealthOutcome("Down", List.of());

src/test/java/com/retailsvc/http/HealthHandlerTest.java

@@ -71,13 +71,12 @@ void headIsAccepted() throws IOException {
     HttpExchange ex = newExchange("HEAD");
     Headers headers = new Headers();
     when(ex.getResponseHeaders()).thenReturn(headers);
-    when(ex.getResponseBody()).thenReturn(new ByteArrayOutputStream());
+    ByteArrayOutputStream body = new ByteArrayOutputStream();
+    when(ex.getResponseBody()).thenReturn(body);
 
     Handlers.healthHandler(() -> new HealthOutcome("Up", List.of())).handle(ex);
 
-    verify(ex)
-        .sendResponseHeaders(
-            eq(HTTP_OK), eq((long) "{\"outcome\":\"Up\",\"dependencies\":[]}".length()));
+    verify(ex).sendResponseHeaders(eq(HTTP_OK), eq((long) body.size()));
   }
 
   @Test