public static <T> Set<T> mergeSet(final Set<T> set1, final Set<T> set2) {
        set1.addAll(set2);
        return set1;
    }
merge.

@param set1 merge to.
@param set2 merge from.
@param <T>  type
@return collection1
shenyu-common/src/main/java/org/apache/shenyu/common/utils/ListUtil.java