code: @Override
      public void removeChild(IGroupMember gm) throws GroupsException {
          String cacheKey = gm.getEntityIdentifier().getKey();
  
          if (getAddedMembers().containsKey(cacheKey)) {
              getAddedMembers().remove(cacheKey);
          } else {
              getRemovedMembers().put(cacheKey, gm);
          }
  
          primRemoveMember(gm);
      }
docs: Removes <code>IGroupMember</code> gm from our member <code>Map</code> and, conversely, remove
  this from gm's group <code>Map</code>. Remember that we have removed it so we can update the
  database, if necessary.
  
  @param gm org.apereo.portal.groups.IGroupMember