code: func (a *Assertions) NotNilf(object interface{}, msg string, args ...interface{}) {
  	if h, ok := a.t.(tHelper); ok {
  		h.Helper()
  	}
  	NotNilf(a.t, object, msg, args...)
  }
docs: // NotNilf asserts that the specified object is not nil.
  //
  //    a.NotNilf(err, "error message %s", "formatted")