src/Executor/ReferenceExecutor.php
private function buildResponse($data)
    {
        if ($this->isPromise($data)) {
            return $data->then(function ($resolved) {
                return $this->buildResponse($resolved);
            });
        }
        if ($data !== null) {
            $data = (array) $data;
        }

        return new ExecutionResult($data, $this->exeContext->errors);
    }
private function buildResponse($data)
    {
        if ($this->isPromise($data)) {
            return $data->then(function ($resolved) {
                return $this->buildResponse($resolved);
            });
        }
        if ($data !== null) {
            $data = (array) $data;
        }

        return new ExecutionResult($data, $this->exeContext->errors);
    }
@param mixed|Promise|null $data

@return ExecutionResult|Promise