Added null check for primitives

bin/tdlib_gen.dart

@@ -198,11 +198,19 @@ String findFromJsonHandling(
     'int53': 'int',
     'Bool': 'bool',
   };
+  final predefinedDefault = {
+    'double': '0',
+    'string': "''",
+    'int32': '0',
+    'int53': '0',
+    'Bool': 'false',
+  };
+
   if (predefined.containsKey(type)) {
-    return '$varAccess as ${predefined[type]}';
+    return '($varAccess as ${predefined[type]}?) ?? ${predefinedDefault[type]}';
   }
   else if (type == 'int64') {
-    return 'int.parse($varAccess)';
+    return "int.parse($varAccess ?? '0')";
   }
   else if (type == 'bytes') {
     return 'base64.decode($varAccess)';