@Deprecated
    public static boolean isEmpty(PrincipalCollection principals) {
        return principals == null || principals.isEmpty();
    }
Returns {@code true} if the specified {@code PrincipalCollection} is {@code null} or
{@link PrincipalCollection#isEmpty empty}, {@code false} otherwise.

@param principals the principals to check.
@return {@code true} if the specified {@code PrincipalCollection} is {@code null} or
{@link PrincipalCollection#isEmpty empty}, {@code false} otherwise.
@since 1.0
@deprecated Use PrincipalCollection.isEmpty() directly.
core/src/main/java/org/apache/shiro/util/CollectionUtils.java