`verdi node graph generate` error for missing PK is not correctly handled and help page is wrong

[agoscinski]

Describe the bug / Steps to reproduce / Expected behavior

• Error for missing is PK not properly handled

  $ verdi node graph generate
  Traceback (most recent call last):
  File "/home/alexgo/micromamba/envs/aiida-dev/bin/verdi", line 8, in <module>
  sys.exit(verdi())
           ^^^^^^^
  File "/home/alexgo/micromamba/envs/aiida-dev/lib/python3.11/site-packages/click/core.py", line 1157, in __call__
  return self.main(*args, **kwargs)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/alexgo/micromamba/envs/aiida-dev/lib/python3.11/site-packages/click/core.py", line 1078, in main
  rv = self.invoke(ctx)
       ^^^^^^^^^^^^^^^^
  File "/home/alexgo/micromamba/envs/aiida-dev/lib/python3.11/site-packages/click/core.py", line 1688, in invoke
  return _process_result(sub_ctx.command.invoke(sub_ctx))
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/alexgo/micromamba/envs/aiida-dev/lib/python3.11/site-packages/click/core.py", line 1688, in invoke
  return _process_result(sub_ctx.command.invoke(sub_ctx))
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/alexgo/micromamba/envs/aiida-dev/lib/python3.11/site-packages/click/core.py", line 1688, in invoke
  return _process_result(sub_ctx.command.invoke(sub_ctx))
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/alexgo/micromamba/envs/aiida-dev/lib/python3.11/site-packages/click/core.py", line 1434, in invoke
  return ctx.invoke(self.callback, **ctx.params)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/alexgo/micromamba/envs/aiida-dev/lib/python3.11/site-packages/click/core.py", line 783, in invoke
  return __callback(*args, **kwargs)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/alexgo/code/aiida-core/src/aiida/cmdline/utils/decorators.py", line 102, in wrapper
  return wrapped(*args, **kwargs)
         ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/alexgo/code/aiida-core/src/aiida/cmdline/commands/cmd_node.py", line 535, in graph_generate
  pks = '.'.join(str(n.pk) for n in root_nodes)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/alexgo/code/aiida-core/src/aiida/cmdline/commands/cmd_node.py", line 535, in <genexpr>
  pks = '.'.join(str(n.pk) for n in root_nodes)
                     ^^^^
  AttributeError: 'NoneType' object has no attribute 'pk'

  Compare to

  
  $ verdi computer show
  Usage: verdi computer show [OPTIONS] COMPUTER
  Try 'verdi computer show --help' for help.

Error: Missing argument 'COMPUTER'.

The error seems not to be properly handled in the former case.

- The help page of the command is wrong
```bash
$ verdi node graph generate --help
Usage: verdi node graph generate [OPTIONS] [--] [ROOT_NODE] OUTPUT_FILE

  Generate a graph from one or multiple root nodes.
[...]

Again comparing it with other commands, I interpret [ROOT_NODE] as optional, but it is not, it is the OUTPUT_FILE which is optional. Also verdi node graph generate -N 1 output.pdf does not work but one has to do verdi node graph generate -N 1 -O output.pdf

Your environment

• Operating system: Ubuntu 22.04 LTS
• Python version: 3.11

  $ verdi status
  ✔ version:     AiiDA v2.5.1
  ✔ config:      /home/alexgo/code/aiida-core/.aiida
  ✔ profile:     alexgo
  ✔ storage:     SqliteDosStorage[/home/alexgo/code/aiida-core/.aiida/repository/sqlite_dos_f275ff0f10174e8e84c13e82dd5ba452]: open,
  ✔ rabbitmq:    Connected to RabbitMQ v3.8.14 as amqp://guest:guest@127.0.0.1:5672?heartbeat=600

[sphuber]

This is a regression introduced by #6338 which made it possible to specify multiple root nodes using the -N option. Specifying the node positionally was deprecated and had to be made optional, so the help string is correct. It is generated automatically by click by the way.

The problem here is the handling of the case where no root node is specified neither positionally nor with -N.