https://lucene.apache.org/core/5_3_1/core/org/apache/lucene/util/CollectionUtil.html
CollectionUtil (Lucene 5.3.1 API)
luceneapi
https://iplass.org/docs32/javadoc/org/iplass/mtp/util/CollectionUtil.html
CollectionUtil (iPLAss 3.2.42 API)
declaration: package: org.iplass.mtp.util, class: CollectionUtil
api