output: #fixed code
                                @Override
    public Collection<String> getAllTypeNames()
    {
      FqnCache<LocklessLazyVar<M>> fqnCache = _fqnToModel.get();
      if( fqnCache.isEmpty() )
      {
        return Collections.emptySet();
      }
  
      return fqnCache.getFqns();
    }
input: #vulnerable code 
                                @Override
    public Collection<String> getAllTypeNames()
    {
      return _fqnToModel.get().getFqns();
    } 
                              #location 4 
                              #vulnerability type NULL_DEREFERENCE