Check value instead of name for not null when collecting MDC entries?

[jhorstmann]

While reading the code handling MDC values I came across the following snipped in LogbackLogEvent v1.12.0 and was wondering if this is working as intended or whether it should be checking mdcValue instead of mdcName

        for (String mdcName : matchingMdcNames) {
            String mdcValue = getMdcValue(mdcName);
            if (mdcName != null) {
                result.setValue(mdcName, mdcValue);
            }
        }

This is not causing any issues for me at the moment, I'm just curios :)

Make sure that:

• You have read the contribution guidelines.
• You specify the logstash-gelf version and environment so it's obvious which version is affected
• You provide a reproducible test case (either descriptive of as JUnit test) if it's a bug or the expected behavior differs from the actual behavior.

[mp911de]

We should fix that. Smells like a bug. Care to submit a pull request?