code: func completeLeafValue(returnType Leaf, result interface{}) interface{} {
  	serializedResult := returnType.Serialize(result)
  	if isNullish(serializedResult) {
  		return nil
  	}
  	return serializedResult
  }
docs: // completeLeafValue complete a leaf value (Scalar / Enum) by serializing to a valid value, returning nil if serialization is not possible.