[Inference API] Make message content optional in unified API

server/src/main/java/org/elasticsearch/inference/UnifiedCompletionRequest.java

@@ -122,7 +122,12 @@ public record Message(Content content, String role, @Nullable String name, @Null
         );
 
         static {
-            PARSER.declareField(constructorArg(), (p, c) -> parseContent(p), new ParseField("content"), ObjectParser.ValueType.VALUE_ARRAY);
+            PARSER.declareField(
+                optionalConstructorArg(),
+                (p, c) -> parseContent(p),
+                new ParseField("content"),
+                ObjectParser.ValueType.VALUE_ARRAY
+            );
             PARSER.declareString(constructorArg(), new ParseField("role"));
             PARSER.declareString(optionalConstructorArg(), new ParseField("name"));
             PARSER.declareString(optionalConstructorArg(), new ParseField("tool_call_id"));

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/external/request/openai/OpenAiUnifiedChatCompletionRequestEntity.java

@@ -78,6 +78,9 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
                             }
                             builder.endArray();
                         }
+                        case null -> {
+                            // do nothing
+                        }
                     }
 
                     builder.field(ROLE_FIELD, message.role());

x-pack/plugin/inference/src/test/java/org/elasticsearch/xpack/inference/external/request/openai/OpenAiUnifiedChatCompletionRequestEntityTests.java

@@ -702,124 +702,6 @@ public void testSerializationWithBooleanFields() throws IOException {
         assertJsonEquals(expectedJsonFalse, jsonStringFalse);
     }
 
-    // 9. Serialization with Missing Required Fields
-    // Test with missing required fields to ensure appropriate exceptions are thrown.
-    public void testSerializationWithMissingRequiredFields() {
-        // Create a message with missing content (required field)
-        UnifiedCompletionRequest.Message message = new UnifiedCompletionRequest.Message(
-            null, // missing content
-            OpenAiUnifiedChatCompletionRequestEntity.USER_FIELD,
-            null,
-            null,
-            null
-        );
-        var messageList = new ArrayList<UnifiedCompletionRequest.Message>();
-        messageList.add(message);
-        // Create the unified request
-        UnifiedCompletionRequest unifiedRequest = new UnifiedCompletionRequest(
-            messageList,
-            null, // model
-            null, // maxCompletionTokens
-            null, // stop
-            null, // temperature
-            null, // toolChoice
-            null, // tools
-            null  // topP
-        );
-
-        // Create the unified chat input
-        UnifiedChatInput unifiedChatInput = new UnifiedChatInput(unifiedRequest, true);
-
-        OpenAiChatCompletionModel model = createChatCompletionModel("test-endpoint", "organizationId", "api-key", "model-name", null);
-
-        // Create the entity
-        OpenAiUnifiedChatCompletionRequestEntity entity = new OpenAiUnifiedChatCompletionRequestEntity(unifiedChatInput, model);
-
-        // Attempt to serialize to XContent and expect an exception
-        try {
-            XContentBuilder builder = JsonXContent.contentBuilder();
-            entity.toXContent(builder, ToXContent.EMPTY_PARAMS);
-            fail("Expected an exception due to missing required fields");
-        } catch (NullPointerException | IOException e) {
-            // Expected exception
-        }
-    }
-
-    // 10. Serialization with Mixed Valid and Invalid Data
-    // Test with a mix of valid and invalid data to ensure the serializer handles it gracefully.
-    public void testSerializationWithMixedValidAndInvalidData() throws IOException {
-        // Create a valid message
-        UnifiedCompletionRequest.Message validMessage = new UnifiedCompletionRequest.Message(
-            new UnifiedCompletionRequest.ContentString("Valid content"),
-            OpenAiUnifiedChatCompletionRequestEntity.USER_FIELD,
-            "validName",
-            "validToolCallId",
-            Collections.singletonList(
-                new UnifiedCompletionRequest.ToolCall(
-                    "validId",
-                    new UnifiedCompletionRequest.ToolCall.FunctionField("validArguments", "validFunctionName"),
-                    "validType"
-                )
-            )
-        );
-
-        // Create an invalid message with null content
-        UnifiedCompletionRequest.Message invalidMessage = new UnifiedCompletionRequest.Message(
-            null, // invalid content
-            OpenAiUnifiedChatCompletionRequestEntity.USER_FIELD,
-            "invalidName",
-            "invalidToolCallId",
-            Collections.singletonList(
-                new UnifiedCompletionRequest.ToolCall(
-                    "invalidId",
-                    new UnifiedCompletionRequest.ToolCall.FunctionField("invalidArguments", "invalidFunctionName"),
-                    "invalidType"
-                )
-            )
-        );
-        var messageList = new ArrayList<UnifiedCompletionRequest.Message>();
-        messageList.add(validMessage);
-        messageList.add(invalidMessage);
-        // Create the unified request with both valid and invalid messages
-        UnifiedCompletionRequest unifiedRequest = new UnifiedCompletionRequest(
-            messageList,
-            "model-name",
-            100L, // maxCompletionTokens
-            Collections.singletonList("stop"),
-            0.9f, // temperature
-            new UnifiedCompletionRequest.ToolChoiceString("tool_choice"),
-            Collections.singletonList(
-                new UnifiedCompletionRequest.Tool(
-                    "type",
-                    new UnifiedCompletionRequest.Tool.FunctionField(
-                        "Fetches the weather in the given location",
-                        "get_weather",
-                        createParameters(),
-                        true
-                    )
-                )
-            ),
-            0.8f // topP
-        );
-
-        // Create the unified chat input
-        UnifiedChatInput unifiedChatInput = new UnifiedChatInput(unifiedRequest, true);
-
-        OpenAiChatCompletionModel model = createChatCompletionModel("test-endpoint", "organizationId", "api-key", "model-name", null);
-
-        // Create the entity
-        OpenAiUnifiedChatCompletionRequestEntity entity = new OpenAiUnifiedChatCompletionRequestEntity(unifiedChatInput, model);
-
-        // Serialize to XContent and verify
-        try {
-            XContentBuilder builder = JsonXContent.contentBuilder();
-            entity.toXContent(builder, ToXContent.EMPTY_PARAMS);
-            fail("Expected an exception due to invalid data");
-        } catch (NullPointerException | IOException e) {
-            // Expected exception
-        }
-    }
-
     public static Map<String, Object> createParameters() {
         Map<String, Object> parameters = new LinkedHashMap<>();
         parameters.put("type", "object");