Error

{
  "graphQLErrors": [
    {
      "message": "GraphQL.ExecutionError: Variable '$comnum' is invalid. Received a null input for a non-null field. ---> GraphQL.Execution.InvalidValueException: Variable '$comnum' is invalid. Received a null input for a non-null field.\r\n   at GraphQL.Execution.ExecutionHelper.AssertValidValue(ISchema schema, IGraphType type, Object input, String fieldName)\r\n   at GraphQL.Execution.ExecutionHelper.GetVariableValue(Document document, ISchema schema, VariableDefinition variable, Object input)\r\n   at GraphQL.Execution.ExecutionHelper.GetVariableValues(Document document, ISchema schema, VariableDefinitions variableDefinitions, Inputs inputs)\r\n   at GraphQL.DocumentExecuter.BuildExecutionContext(ISchema schema, Object root, Document document, Operation operation, Inputs inputs, Object userContext, CancellationToken cancellationToken, Metrics metrics, IEnumerable`1 listeners, Boolean throwOnUnhandledException)\r\n   at GraphQL.DocumentExecuter.<ExecuteAsync>d__8.MoveNext()\r\n   --- End of inner exception stack trace ---",
      "extensions": {
        "code": "INVALID_VALUE"
      }
    }
  ],
  "clientErrors": [],
  "networkError": null,
  "message": "GraphQL.ExecutionError: Variable '$comnum' is invalid. Received a null input for a non-null field. ---> GraphQL.Execution.InvalidValueException: Variable '$comnum' is invalid. Received a null input for a non-null field.\r\n   at GraphQL.Execution.ExecutionHelper.AssertValidValue(ISchema schema, IGraphType type, Object input, String fieldName)\r\n   at GraphQL.Execution.ExecutionHelper.GetVariableValue(Document document, ISchema schema, VariableDefinition variable, Object input)\r\n   at GraphQL.Execution.ExecutionHelper.GetVariableValues(Document document, ISchema schema, VariableDefinitions variableDefinitions, Inputs inputs)\r\n   at GraphQL.DocumentExecuter.BuildExecutionContext(ISchema schema, Object root, Document document, Operation operation, Inputs inputs, Object userContext, CancellationToken cancellationToken, Metrics metrics, IEnumerable`1 listeners, Boolean throwOnUnhandledException)\r\n   at GraphQL.DocumentExecuter.<ExecuteAsync>d__8.MoveNext()\r\n   --- End of inner exception stack trace ---"
}