[6.0.x] Fix --help crash on add_ini(.., help='') and improve message on help=None (#7427)

changelog/7394.bugfix.rst

@@ -0,0 +1,2 @@
+Passing an empty ``help`` value to ``Parser.add_option`` is now accepted instead of crashing when running ``pytest --help``.
+Passing ``None`` raises a more informative ``TypeError``.

src/_pytest/helpconfig.py

@@ -170,6 +170,8 @@ def showhelp(config: Config) -> None:
         help, type, default = config._parser._inidict[name]
         if type is None:
             type = "string"
+        if help is None:
+            raise TypeError("help argument cannot be None for {}".format(name))
         spec = "{} ({}):".format(name, type)
         tw.write("  %s" % spec)
         spec_len = len(spec)
@@ -191,9 +193,10 @@ def showhelp(config: Config) -> None:
             tw.write(" " * (indent_len - spec_len - 2))
             wrapped = textwrap.wrap(help, columns - indent_len, break_on_hyphens=False)
 
-            tw.line(wrapped[0])
-            for line in wrapped[1:]:
-                tw.line(indent + line)
+            if wrapped:
+                tw.line(wrapped[0])
+                for line in wrapped[1:]:
+                    tw.line(indent + line)
 
     tw.line()
     tw.line("environment variables:")

testing/test_helpconfig.py

@@ -38,6 +38,41 @@ def test_help(testdir):
     )
 
 
+def test_none_help_param_raises_exception(testdir):
+    """Tests a None help param raises a TypeError.
+    """
+    testdir.makeconftest(
+        """
+        def pytest_addoption(parser):
+            parser.addini("test_ini", None, default=True, type="bool")
+    """
+    )
+    result = testdir.runpytest("--help")
+    result.stderr.fnmatch_lines(
+        ["*TypeError: help argument cannot be None for test_ini*"]
+    )
+
+
+def test_empty_help_param(testdir):
+    """Tests an empty help param is displayed correctly.
+    """
+    testdir.makeconftest(
+        """
+        def pytest_addoption(parser):
+            parser.addini("test_ini", "", default=True, type="bool")
+    """
+    )
+    result = testdir.runpytest("--help")
+    assert result.ret == 0
+    lines = [
+        "  required_plugins (args):",
+        "                        plugins that must be present for pytest to run*",
+        "  test_ini (bool):*",
+        "environment variables:",
+    ]
+    result.stdout.fnmatch_lines(lines, consecutive=True)
+
+
 def test_hookvalidation_unknown(testdir):
     testdir.makeconftest(
         """