fix(api): do not include null values in ModelMutations.create

packages/api/amplify_api/lib/src/graphql/factories/graphql_request_factory.dart

@@ -281,7 +281,10 @@ class GraphQLRequestFactory {
   ///
   /// When the model has a parent via a belongsTo, the id from the parent is added
   /// as a field similar to "blogID" where the value is `post.blog.id`.
-  Map<String, dynamic> buildInputVariableForMutations(Model model) {
+  Map<String, dynamic> buildInputVariableForMutations(
+    Model model, {
+    required GraphQLRequestOperation operation,
+  }) {
     final schema =
         getModelSchemaByModelName(model.getInstanceType().modelName(), null);
     final modelJson = model.toJson();
@@ -303,10 +306,17 @@ class GraphQLRequestFactory {
       }
     }
 
-    // Remove any relational fields or readonly.
+    // Remove some fields from input.
     final fieldsToRemove = schema.fields!.entries
         .where(
-          (entry) => entry.value.association != null || entry.value.isReadOnly,
+          (entry) =>
+              // relational fields
+              entry.value.association != null ||
+              // read-only
+              entry.value.isReadOnly ||
+              // null values on create operations
+              (operation == GraphQLRequestOperation.create &&
+                  modelJson[entry.value.name] == null),
         )
         .map((entry) => entry.key)
         .toSet();

packages/api/amplify_api/lib/src/graphql/factories/model_mutations_factory.dart

@@ -22,8 +22,10 @@ class ModelMutationsFactory extends ModelMutationsInterface {
     APIAuthorizationType? authorizationMode,
     Map<String, String>? headers,
   }) {
-    final input =
-        GraphQLRequestFactory.instance.buildInputVariableForMutations(model);
+    final input = GraphQLRequestFactory.instance.buildInputVariableForMutations(
+      model,
+      operation: GraphQLRequestOperation.create,
+    );
     // Does not use buildVariablesForMutationRequest because creations don't have conditions.
     final variables = {'input': input};
 
@@ -96,8 +98,10 @@ class ModelMutationsFactory extends ModelMutationsInterface {
   }) {
     final condition = GraphQLRequestFactory.instance
         .queryPredicateToGraphQLFilter(where, model.getInstanceType());
-    final input =
-        GraphQLRequestFactory.instance.buildInputVariableForMutations(model);
+    final input = GraphQLRequestFactory.instance.buildInputVariableForMutations(
+      model,
+      operation: GraphQLRequestOperation.update,
+    );
 
     final variables = GraphQLRequestFactory.instance
         .buildVariablesForMutationRequest(input: input, condition: condition);

packages/api/amplify_api/test/graphql_helpers_test.dart

@@ -378,8 +378,6 @@ void main() {
             'id': id,
             'name': name,
             'createdAt': time,
-            'file': null,
-            'files': null
           }
         };
         const expectedDoc =
@@ -393,6 +391,18 @@ void main() {
         expect(req.decodePath, 'createBlog');
       });
 
+      test(
+          'ModelMutations.create() should not include null fields in input variable',
+          () {
+        const name = 'Test Blog';
+
+        final Blog blog = Blog(name: name);
+        final GraphQLRequest<Blog> req = ModelMutations.create<Blog>(blog);
+        final inputVariable = req.variables['input'] as Map<String, dynamic>;
+
+        expect(inputVariable.containsKey('file'), isFalse);
+      });
+
       test(
           'ModelMutations.create() should build a valid request for a model with a parent',
           () {
@@ -413,8 +423,6 @@ void main() {
             'id': postId,
             'title': title,
             'rating': rating,
-            'created': null,
-            'likeCount': null,
             'blogID': blogId
           }
         };