according to my introduction to logic (or was it structired programming? cant remember) class, doing that is considered "defensive programming" and isn't a good practice.
to clarify, i think they mean doing checks like that when they arent needed. if the excercise says the input will always be a valid string, then you shouldnt do a check for that

Its allways better to check like
if(name == null) throw new IllegalArgumentException("name must not be null");
even if the description says that only valid strings appear

Names given are always valid strings.