fix(logging): preserve log messages with the literal string "None"

[o6ivp]

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Fixes #17339 🦕

What

_format_and_parse_message (in handlers/handlers.py) treated any record whose formatted output equaled the string "None" as empty content, returning None (or omitting the message field when json_fields were present).

This also dropped a legitimate user message consisting of the literal string "None":

logging.getLogger().info("None")   # payload silently became empty / None

Why

The empty-content branch is intended to cover a record whose msg is the Python object None, which logging.Formatter renders as the string "None". Comparing the formatted string against "None" cannot distinguish that case from a user who logged the literal text "None", so real content was lost.

How

Detect the empty case from record.msg is None (before formatting) and the formatted output being "None", instead of from the formatted output alone. This preserves the existing behavior for msg=None (with and without a custom formatter) while keeping a genuine "None" string.

Behavior matrix:

record.msg	formatter	before	after
None	none	None	None (unchanged)
None	custom ("name: %(name)s")	"name: logname"	"name: logname" (unchanged)
"None" (str)	none	None ❌ dropped	"None" ✅ preserved

Tests

Added two unit tests (test_literal_none_string_preserved, test_literal_none_string_preserved_with_json_fields). All tests/unit/handlers/ tests pass (177 passed) and ruff format --check is clean.

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[gemini-code-assist]

Code Review

This pull request fixes an issue where a literal string message of "None" was incorrectly treated as an empty message and dropped. It introduces a check to ensure that only records where the original message (record.msg) is actually the Python None object are treated as empty, while preserving the literal string "None". Unit tests have been added to verify this behavior. There are no review comments to address, and the changes look solid.