Fix execution summary for optional parameters

[starhel]

Description

If an optional parameter has its own next_in_enumeration method, generating a summary ends in an error if the same task has been run both with a value of None and with a proper value for the parameter.

Motivation and Context

import luigi

class A(luigi.ExternalTask):
    def output(self):
        return luigi.LocalTarget("a.txt")

class RecB(luigi.Task):
    step = luigi.OptionalIntParameter(default=None)

    def requires(self):
        step = 3 if self.step is None else self.step
        if step == 0:
            yield self.clone(A)
        else:
            yield self.clone(step=step-1)

    def run(self):
        with self.output().open("w") as f:
            f.write("1")

    def output(self):
        return luigi.LocalTarget(f"b_{self.step}.txt")

luigi.build([RecB()])

Traceback (most recent call last):
  File "/home/astachlewski/tmp/luigi_bug_recursive_graph/bug.py", line 28, in <module>
    luigi.build([RecB()])
  File "/home/astachlewski/tmp/luigi_bug_recursive_graph/venv/lib/python3.10/site-packages/luigi/interface.py", line 243, in build
    luigi_run_result = _schedule_and_run(tasks, worker_scheduler_factory, override_defaults=env_params)
  File "/home/astachlewski/tmp/luigi_bug_recursive_graph/venv/lib/python3.10/site-packages/luigi/interface.py", line 178, in _schedule_and_run
    luigi_run_result = LuigiRunResult(worker, success)
  File "/home/astachlewski/tmp/luigi_bug_recursive_graph/venv/lib/python3.10/site-packages/luigi/execution_summary.py", line 79, in __init__
    self.summary_text = _summary_wrap(_summary_format(summary_dict, worker))
  File "/home/astachlewski/tmp/luigi_bug_recursive_graph/venv/lib/python3.10/site-packages/luigi/execution_summary.py", line 414, in _summary_format
    str_output += '{0}\n'.format(_get_str(group_tasks[status], status in _PENDING_SUB_STATUSES))
  File "/home/astachlewski/tmp/luigi_bug_recursive_graph/venv/lib/python3.10/site-packages/luigi/execution_summary.py", line 196, in _get_str
    first, last = _ranging_attributes(attributes, param_class)
  File "/home/astachlewski/tmp/luigi_bug_recursive_graph/venv/lib/python3.10/site-packages/luigi/execution_summary.py", line 261, in _ranging_attributes
    next_attributes = {param_class.next_in_enumeration(attribute) for attribute in attributes}
  File "/home/astachlewski/tmp/luigi_bug_recursive_graph/venv/lib/python3.10/site-packages/luigi/execution_summary.py", line 261, in <setcomp>
    next_attributes = {param_class.next_in_enumeration(attribute) for attribute in attributes}
  File "/home/astachlewski/tmp/luigi_bug_recursive_graph/venv/lib/python3.10/site-packages/luigi/parameter.py", line 686, in next_in_enumeration
    return value + 1
TypeError: unsupported operand type(s) for +: 'NoneType' and 'int'

Have you tested this? If so, how?

Automated tests as well as running the above code.

[starhel]

I've also fixed some broken test for jsonschema (as order of validation is changed in newest version).