fix(generator): Json field short input type selection

Refs: #209 #216

bin/src/generator.dart

@@ -328,19 +328,31 @@ extension InputObjectTypesGenerator on PrismaDartClientGenerator {
 
   /// Build field type
   code.Reference _buildFieldType(dmmf.SchemaArg field) {
-    final types = field.inputTypes;
+    /// TODO: bug https://github.com/odroe/prisma-dart/issues/209
+    withoutJsonValueInput(String name) {
+      if (name == 'NullableJsonNullValueInput') return false;
+      if (name == 'JsonNullValueInput') return false;
+
+      return true;
+    }
+
+    final types = field.inputTypes.where((element) => element.type.when<bool>(
+          string: withoutJsonValueInput,
+          input: (input) => withoutJsonValueInput(input.name),
+          enum_: (enum_) => withoutJsonValueInput(enum_.name),
+        ));
 
     // If the types is a single type, return it.
     if (types.length == 1) {
-      final type = field.inputTypes.first.type.when<String>(
+      final type = types.first.type.when<String>(
         string: (value) => value,
         input: (type) => type.name,
         enum_: (type) => type.name,
       );
 
       return scalar(
         type,
-        location: field.inputTypes.first.location,
+        location: types.first.location,
         isNullable: !field.isRequired,
         isList: field.inputTypes.first.isList,
       );

bin/src/scalars.dart

@@ -13,7 +13,7 @@ final Map<String, Reference> scalarReferences = {
   'int': refer('int'),
   'bigint': refer('BigInt'),
   'boolean': refer('bool'),
-  'json': refer('dynamic'),
+  'json': refer('Object'),
   'bytes': TypeReference((TypeReferenceBuilder updates) {
     updates.symbol = 'List';
     updates.types.add(Reference('int'));