I'm used to Java's String where we can pass null rather than "" for special meanings, such as use a default value.

In Go, string is a primitive type, so I cannot pass nil (null) to a parameter that requires a string.

I could write the function using pointer type, like this:

func f(s *string)

so caller can call that function either as

f(nil)

or

// not so elegant
temp := "hello";
f(&temp)

but the following is unfortunately not allowed:

// elegant but disallowed
f(&"hello");

What is the best way to have a parameter that receives either a string or nil?