How to get detailed :error message from mutate filter?

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?