Upgrade Logstash : mutate filter is not working well

Following the logstash migrating from 1.4.2 version to 1.5.3 version when I do an uppercase in the mutate filter on a field ending with numeric value the field becomes nil.
Yet, before that worked.
How can I fix it ?

My logstash config :
filter {
mutate {
convert => ["my_field","string"]
uppercase => ["my_field"]

That's the same thing with lowercase and kibana says to me : objects in arrays are not well supported.
Although this is just a simple string not an array

Nobody has encountered this problem ?

@Hornov, Facing the issue now. Pretty upset. :rage: The behavior is inconsistent.
In the filter, I grok first. Follow by mutate. It will work. But randomly mutate.uppercase=> [field] will cause that field to be null/nil whatever. It is corrupting my data!

I am running on windows and linux.

Ok. Some digging and found this piece of information. So just need to update the plugin