Detailed error messages from mutate are not logged anywhere. When the mutate filter raises a logstash.agent.configuration.invalid_plugin_register exception it includes in the raise a detailed exception such as
"Invalid conversion type '#{type}', expected one of '#{valid_conversions.join(',')}'"
or
"Invalid gsub configuration #{[field, needle, replacement]}. gsub requires 3 non-nil elements per config entry"
But these never show up in the log file. Can the user configure the logging to make these appear?