code: private EntryImpl checkOldName(String baseName) {
          EntryImpl e = (EntryImpl) name2entry.get(baseName);
          if (e == null) {
              throw new IllegalArgumentException("Filter not found:" + baseName);
          }
          return e;
      }
docs: Throws an exception when the specified filter name is not registered in this chain.
  
  @return An filter entry with the specified name.