code: func ValidateNonEmptySelector(selectorMap map[string]string, fldPath *field.Path) field.ErrorList {
  	allErrs := field.ErrorList{}
  	selector := labels.Set(selectorMap).AsSelector()
  	if selector.Empty() {
  		allErrs = append(allErrs, field.Required(fldPath, ""))
  	}
  	return allErrs
  }
docs: // Validates that the given selector is non-empty.