// requireNonNull is safe because the endpoint pair comes from the graph.
          subgraph.putEdgeValue(
              node,
              successorNode,
              requireNonNull(graph.edgeValueOrDefault(node, successorNode, null)));
        }
      }
    }
    return subgraph;
  }

  /**

```mermaid
flowchart TB
    subgraph stone-project[philosophers-stone project]
        stone(philosophers-stone) --->|requires| harry-1
        subgraph venv1[.venv]
            harry-1[harry v1]
        end
    end
    subgraph azkaban-project[prisoner-of-azkaban project]
        azkaban(prisoner-of-azkaban) --->|requires| harry-3
        subgraph venv2[.venv]
            harry-3[harry v3]
        end

Example:

Source (English):

```mermaid
flowchart LR
    subgraph global[global env]
        harry-1[harry v1]
    end
    subgraph stone-project[philosophers-stone project]
        stone(philosophers-stone) -->|requires| harry-1
    end
```

Existing translation (German) - has three translations:

```mermaid
flowchart LR
    subgraph global[globale Umgebung]
        harry-1[harry v1]
    end

这样，每个工程都会有自己的虚拟环境（`.venv` 目录），其中包含自己的软件包。

```mermaid
flowchart TB
    subgraph stone-project[工程 philosophers-stone]
        stone(philosophers-stone) --->|需要| harry-1
        subgraph venv1[.venv]
            harry-1[harry v1]
        end
    end
    subgraph azkaban-project[工程 prisoner-of-azkaban]
        azkaban(prisoner-of-azkaban) --->|需要| harry-3
        subgraph venv2[.venv]
            harry-3[harry v3]
        end
    end

```mermaid
flowchart TB
    subgraph stone-project[philosophers-stone project]
        stone(philosophers-stone) --->|requires| harry-1
        subgraph venv1[.venv]
            harry-1[harry v1]
        end
    end
    subgraph azkaban-project[prisoner-of-azkaban project]
        azkaban(prisoner-of-azkaban) --->|requires| harry-3
        subgraph venv2[.venv]
            harry-3[harry v3]
        end

 * based on your answers to the following questions:
 *
 * <ol>
 *   <li>Is there only one path to any node that's reachable from any start node? (If so, the graph
 *       to be traversed is a tree or forest even if it is a subgraph of a graph which is neither.)
 *   <li>Are the node objects' implementations of {@code equals()}/{@code hashCode()} <a
 *       href="https://github.com/google/guava/wiki/GraphsExplained#non-recursiveness">recursive</a>?
 * </ol>

    // During execution:
    //   * task:0 processes main function `VariableAddFunctionWithGraphError`
    //     and places the 'read0_maybe_with_graph_error' op on task:2
    //   * task:0 partitions the main function with a subgraph containing
    //     'read0_maybe_with_graph_error' sent to task:2
    //   * task:2 graph pass reports an error when it sees
    //     'read0_maybe_with_graph_error' with dev2_name

```mermaid
flowchart TB
    subgraph stone-project[philosophers-stone project]
        stone(philosophers-stone) --->|requires| harry-1
        subgraph venv1[.venv]
            harry-1[harry v1]
        end
    end
    subgraph azkaban-project[prisoner-of-azkaban project]
        azkaban(prisoner-of-azkaban) --->|requires| harry-3
        subgraph venv2[.venv]
            harry-3[harry v3]
        end

```mermaid
flowchart TB
    subgraph stone-project[philosophers-stone project]
        stone(philosophers-stone) --->|requires| harry-1
        subgraph venv1[.venv]
            harry-1[harry v1]
        end
    end
    subgraph azkaban-project[prisoner-of-azkaban project]
        azkaban(prisoner-of-azkaban) --->|requires| harry-3
        subgraph venv2[.venv]
            harry-3[harry v3]
        end

```mermaid
flowchart TB
    subgraph stone-project[philosophers-stone-Projekt]
        stone(philosophers-stone) --->|benötigt| harry-1
        subgraph venv1[.venv]
            harry-1[harry v1]
        end
    end
    subgraph azkaban-project[prisoner-of-azkaban-Projekt]
        azkaban(prisoner-of-azkaban) --->|benötigt| harry-3
        subgraph venv2[.venv]
            harry-3[harry v3]
        end