Logging the literal string "None" is silently dropped (payload becomes empty)

从 google/cloud/logging_v2/handlers/handlers.py 中的 _format_and_parse_message 开始，然后运行针对 "None"、"hello" 和 "" 提供的 LogRecord 复现。完成的标准是：字面字符串 "None" 保留在解析后的 payload 中，同时现有用例保留其预期结果。

• I determined this is the correct repository in which to report this bug.

Summary of the issue

Context
Using CloudLoggingHandler / StructuredLogHandler via the Python standard logging module, I logged the string "None" (e.g. logging.getLogger().info("None")).

Expected Behavior:
The log entry payload should contain the text "None", just like any other string.

Actual Behavior:
The message is silently dropped: the parsed payload becomes None (empty), so the log content disappears.

API client name and version

google-cloud-logging v3.15.0 (also present on current main)

Reproduction steps: code

import logging
from google.cloud.logging_v2.handlers import handlers as H

class FakeHandler(logging.Handler):
    pass

h = FakeHandler()
h.setFormatter(logging.Formatter())

def rec(msg):
    return logging.LogRecord("n", logging.INFO, "p", 1, msg, (), None)

for msg in ["None", "hello", ""]:
    print(repr(msg), "->", repr(H._format_and_parse_message(rec(msg), h)))

Reproduction steps: actual results

'None'  -> None      # the user's message is dropped
'hello' -> 'hello'
''      -> ''

Reproduction steps: expected results

'None'  -> 'None'    # the literal string should be preserved
'hello' -> 'hello'
''      -> ''

OS & version + platform

Any (logic bug, platform-independent)

Python environment

Python 3.12

Additional context

Root cause in google/cloud/logging_v2/handlers/handlers.py (_format_and_parse_message):

if message != "None":
    passed_json_fields["message"] = message
...
return message if message != "None" else None

The intent appears to be detecting a record whose msg is the Python object None (which logging.Formatter renders as the string "None"). But comparing the formatted string against "None" also matches a legitimate user message of the literal text "None", dropping it. Detecting emptiness from record.msg is None (before formatting) rather than from the formatted output would avoid the false positive.