Debug logger does not print if the formatted message is empty, even if an exception is provided

[colejohnson66]

Description

In the DebugLogger implementation, it does not log anything to the debug output if the formatted message is blank, even if an exception is provided.

runtime/src/libraries/Microsoft.Extensions.Logging.Debug/src/DebugLogger.cs

Lines 39 to 63 in ab70886

	public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception? exception, Func<TState, Exception?, string> formatter)
	{
	if (!IsEnabled(logLevel))
	{
	return;
	}
	ArgumentNullException.ThrowIfNull(formatter);
	string message = formatter(state, exception);
	if (string.IsNullOrEmpty(message))
	{
	return;
	}
	message = $"{logLevel}: {message}";
	if (exception != null)
	{
	message += Environment.NewLine + Environment.NewLine + exception;
	}
	DebugWriteLine(message, _name);
	}

Reproduction Steps

ILogger logger = new DebugLoggerProvider.CreateLogger("test");
new TestClass(logger).TestMethod();

public static partial class TestClass(ILogger logger)
{
    [LoggerMessage(LogLevel.Error)]
    private partial void LogException(Exception ex);

    public static void Method()
    {
        try
        {
            throw new InvalidOperationException("testing!");
        }
        catch (Exception ex)
        {
            LogException(ex);          // using source generator
            logger.LogError(ex, null); // "old"-style
        }
    }
}

Expected behavior

I see a debug output of the exception.

Actual behavior

Nothing is printed to the output because the message is empty.

Regression?

No response

Known Workarounds

Provide a dummy message to the source generator or "old"-style extension method:

[LoggerMessage(LogLevel.Error, "Exception.")]
private partial void LogException(Exception ex);

// --OR--

logger.LogError(ex, "Exception.");

Configuration

No response

Other information

The logger should only "fail" to write (i.e., do nothing) if neither a message nor an exception is provided.

Alternatively, if this is the desired behavior of ILogger, it should be made clear, possibly with an analyzer, that an exception with no message on LogError is a bad idea.

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[tarekgh]

@colejohnson66 thanks for reporting it. Are you interested in submitting a PR to fix it?