private ProcedureEvent<?> getMetaAssignEvent(RegionInfo metaRegionInfo) {
    assert isMetaRegion(metaRegionInfo) : "unexpected non-meta region " + metaRegionInfo;
    // TODO: handle multiple meta.
    return metaAssignEvent;
  }
Notice that this event does not mean the AM has already finished region state rebuilding. See
the comment of {@link #isMetaAssigned()} for more details.
@see #isMetaAssigned()
hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/AssignmentManager.java