Print <undetermined location> instead of None for warnings

changelog/3563.bugfix.rst

@@ -0,0 +1 @@
+Warnings without ``location`` were reported as ``None``.  This is corrected to now report ``<undetermined location>``.

src/_pytest/terminal.py

@@ -682,7 +682,7 @@ class TerminalReporter(object):
 
             self.write_sep("=", "warnings summary", yellow=True, bold=False)
             for location, warning_records in grouped:
-                self._tw.line(str(location) or "<undetermined location>")
+                self._tw.line(str(location) if location else "<undetermined location>")
                 for w in warning_records:
                     lines = w.message.splitlines()
                     indented = "\n".join("  " + x for x in lines)

testing/test_terminal.py

@@ -1025,7 +1025,10 @@ def test_terminal_summary_warnings_are_displayed(testdir):
     """
     )
     result = testdir.runpytest("-rw")
-    result.stdout.fnmatch_lines(["*internal warning", "*== 1 warnings in *"])
+    result.stdout.fnmatch_lines(
+        ["<undetermined location>", "*internal warning", "*== 1 warnings in *"]
+    )
+    assert "None" not in result.stdout.str()
 
 
 @pytest.mark.parametrize(