code: Map<String, Graph> getGraphCache(boolean includeUserDefined, boolean includeAutoGenerated) {
      return getCache(userGraphCache, autoGraphCache, includeUserDefined, includeAutoGenerated);
    }
docs: Returns a cache containing a mapping from variables to graphs.
  
  @param includeUserDefined include user-defined variables
  @param includeAutoGenerated include auto-generated variables
  
  @return immutable graph cache