code: func Nilf(t TestingT, object interface{}, msg string, args ...interface{}) bool {
  	if h, ok := t.(tHelper); ok {
  		h.Helper()
  	}
  	return Nil(t, object, append([]interface{}{msg}, args...)...)
  }
docs: // Nilf asserts that the specified object is nil.
  //
  //    assert.Nilf(t, err, "error message %s", "formatted")