Given a java class with a setter taking a non-nullable value, and kotlin extension function with a nullable parameter, what's idiomatic way to call the setter if the param is non-null?

fun MyPojo.init(fieldName: String? = null) {
            fieldName?.let(::setFieldName)
            fieldName?.also { setFieldName(it) }
            fieldName?.also { this.fieldName = it }
            if(fieldName != null) setFieldName(fieldName)
            if(fieldName != null) this.fieldName = fieldName
}

Not sure Kotlin is opinionated enough for any of them to be ideomatic. I would prefer either because of autocasting

fieldName?.also(::setFieldName)
fieldName?.also { setFieldName(it) }

in the case of

fieldName?.also { setFieldName(it) }

is it not better to use the property syntax?

Missed that. Yes that would probably be more ideomatic

Personally, I find

if(fieldName != null) this.fieldName = fieldName

to be the solution that's easiest to understand at a glance. I mostly use

let

and

also

as part of longer chains as otherwise I don't always see an advantage in using them.