3.0.6: got this error after webpacking code when using logLevelFilter appender :
TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received type undefined

I only succeed in fixing it after pre-loading logLevelFilter appender in lib/appenders/index.js:16:
coreAppenders.set('logLevelFilter', require('./logLevelFilter'));