#fixed code
                              @Override
  public boolean isTopLevelType( String fqn )
  {
    FqnCache<LocklessLazyVar<M>> fqnCache = _fqnToModel.get();
    if( fqnCache.isEmpty() )
    {
      return false;
    }

    return fqnCache.get( fqn ) != null;
  }
#vulnerable code 
                              @Override
  public boolean isTopLevelType( String fqn )
  {
    return _fqnToModel.get().get( fqn ) != null;
  } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE