How to resolve “does not match function signature” in jsonata.Extension

[FatsLan]

Excuse.
I have defined a jsonata.Extension, for example:

"mandatory": {
Func: func(input string) (string, error) {
if input == "" {
return input, errors.New(" input is required ")
}
return input, nil
},
}

If the parameter is not passed to “input”, how can I make jsonata not report an error?

[tbal999]

remove the errors.New and replace with nil