SOLR-6182: correctly cast managedData as a List<Object> when loading stored RestManager data; solution verified with manual testing only as the unit tests use in-memory storage so will need to re-work the backing store to test this behavior in the unit test; backport to branch_4x
lucene/dev/branches/branch_4x/solr/core/src/java/org/apache/solr/rest/RestManager.java