This inspection reports any instances of Groovy statements which attempts to put GString object as a key to map.
In a general way GString objects are mutable and probably should not be used as keys.
Also, GString entry could not be accessed with java.lang.String object with same value. Example:
def map = [:]
def key = 'foo'
map << ["${key}": 'bar']
assert map[key] == null
New in 2017.1