It is not recommended to use len for empty string test.

A string can be tested for its emptiness either by treating it as a slice and calculating the length of the slice, or by treating it as a string and directly comparing the value. While both produce identical code when compiled, it makes more sense to treat a string as itself, than a slice, for the sake of comparison of values.

Bad practice

len(s) == 0

Recommended

s == ""

The recommended practice is considered more idiomatic in Go.