You can use isNullOrEmpty or its friend isNullOrBlank like so:
if(!s.isNullOrEmpty()){
// s is not empty
}
Both isNullOrEmpty and isNullOrBlank are extension methods on CharSequence? thus you can use them safely with null. Alternatively turn null into false like so:
if(s?.isNotEmpty() ?: false){
// s is not empty
}
you can also do the following
if(s?.isNotEmpty() == true){
// s is not empty
}