fix(statistics): handle exceptions without a traceback in ErrorTracker

[anxkhn]

ErrorTracker._get_file_and_line calls traceback.extract_tb(error.__traceback__)
and then unconditionally reads the last frame with error_traceback[-1]. For an
exception whose __traceback__ is None (for example a freshly constructed
exception that was never raised), extract_tb returns an empty list, so [-1]
raises IndexError.

_get_file_and_line is called from ErrorTracker.add, which is a best-effort
statistics path, so a valid Exception argument that happens to carry no
traceback crashes the tracker instead of being counted.

This guards the empty case: when there are no traceback frames, return an empty
file-and-line string, which is exactly the value the method already returns when
show_file_and_line_number is disabled. That empty value is already handled
everywhere downstream (it is used as the top-level grouping key in add, and
_get_error_repr renders an empty file-and-line as no prefix), so grouping and
the error representation stay correct.

• Guard the empty-traceback case in ErrorTracker._get_file_and_line and return ''.
• Add a regression test that adds a never-raised exception and asserts it is tracked without raising.

Issues

• None (self-contained fix). Related prior hardening in the same class: fix: fix handle error without args in _get_error_message for ErrorTracker #1181.

Testing

• Added test_error_tracker_error_without_traceback in
  tests/unit/_statistics/test_error_tracker.py. It constructs ValueError('Some value error')
  (never raised, so __traceback__ is None), calls await error_tracker.add(...),
  and asserts total == 1, unique_error_count == 1, and that
  get_most_common_errors() reports 'ValueError:Some value error' (name and
  message, with no file:line prefix). The test fails with IndexError on
  master and passes with the fix.
• uv run pytest tests/unit/_statistics/test_error_tracker.py -> 14 passed (offline).
• uv run poe lint -> all checks passed.
• uv run poe type-check on the changed files -> passed. (The full type-check reports
  pre-existing diagnostics only in the unrelated _pydantic_ai module, which needs an
  optional dependency; the changed files are clean.)

Checklist

• CI passed

---

The diff (2 files, +16)

diff --git a/src/crawlee/statistics/_error_tracker.py b/src/crawlee/statistics/_error_tracker.py
index 20f827a..fd4a938 100644
--- a/src/crawlee/statistics/_error_tracker.py
+++ b/src/crawlee/statistics/_error_tracker.py
@@ -107,6 +107,9 @@ class ErrorTracker:
     def _get_file_and_line(self, error: Exception) -> str:
         if self.show_file_and_line_number:
             error_traceback = traceback.extract_tb(error.__traceback__)
+            if not error_traceback:
+                # The exception has no traceback (e.g. it was never raised).
+                return ''
             # Show only the most specific frame.
             return f'{error_traceback[-1].filename.split("/")[-1]}:{error_traceback[-1].lineno}'
         return ''
diff --git a/tests/unit/_statistics/test_error_tracker.py b/tests/unit/_statistics/test_error_tracker.py
index 26f02c5..d0dbac6 100644
--- a/tests/unit/_statistics/test_error_tracker.py
+++ b/tests/unit/_statistics/test_error_tracker.py
@@ -114,3 +114,16 @@ async def test_error_tracker_with_errors_chain() -> None:
             await error_tracker.add(e)
 
     assert error_tracker.get_most_common_errors()[0][0] == 'Zero division error'
+
+
+async def test_error_tracker_error_without_traceback() -> None:
+    """Test that an exception with no traceback (never raised) is tracked without crashing."""
+    error_tracker = ErrorTracker()
+
+    # A freshly constructed exception has `__traceback__` set to None.
+    await error_tracker.add(ValueError('Some value error'))
+
+    assert error_tracker.total == 1
+    assert error_tracker.unique_error_count == 1
+    # With no traceback there is no file and line, so the group has just the name and message.
+    assert error_tracker.get_most_common_errors()[0][0] == 'ValueError:Some value error'