Add boolean support for langchain_core.runnables.graph_mermaid.draw_mermaid_png

[ykoitzsch]

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Feature request

When drawing a graph with conditional edges, there is the possibility to name those edges: graph.add_conditional_edges("branch_a", router, {"branch_b": "branch_b", "branch_c": "branch_c"})

It would be great if it could also handle not just strings but also boolean values such as:
graph.add_conditional_edges("branch_a", return_true_or_false, {True "branch_b", False: "branch_c"})

`

but the library expects a string, tries to split it and thats where it fails when using boolean values.

Motivation

Often there are use-cases where we have 2 paths from a node. Example: determine whether the AI makes a tool call or not:

flow.add_conditional_edges("classify_query", has_tool_calls, { True: "branch_a", False: "branch_b"})

this way, has_tool_calls can be re-used and we don't need a separate methhod for each conditional branch that checks on the same condition.

Proposal (If applicable)

No response