Cannot set the connection character set to utf8mb4

[minusbat]

Mysql by default only supports 3 byte utf-8. You need to use the character set type utf8mb4 to use 4 byte Utf-8. This plugin works fine with 3 byte UTF-8, but with 4 byte it fails with the error:

error_class=Mysql2::Error error="Incorrect string value:

We belive this is because the client connection is set to uttf8 not utf8mb4. We have tried adding 'encoding utf8mb4' to the fluentd config fiile (as specified by the mysql2 docs) but this does not work unfortunately.
Could the connection always be set top utf8mb4 as this would be backward compatible with utf8 and allow this to work correctly ?