log/field.go
func Error(err error) Field {
	return Field{
		key:          "error",
		fieldType:    errorType,
		interfaceVal: err,
	}
}
func Error(err error) Field {
	return Field{
		key:          "error",
		fieldType:    errorType,
		interfaceVal: err,
	}
}
// Error adds an error with the key "error" to a Span.LogFields() record