Fix udf serialization

[andreidan]

No description provided.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@7c0f96c). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #6076   +/-   ##
=========================================
  Coverage          ?   83.02%           
  Complexity        ?    12424           
=========================================
  Files             ?     1436           
  Lines             ?    47065           
  Branches          ?     5799           
=========================================
  Hits              ?    39076           
  Misses            ?     5286           
  Partials          ?     2703

Impacted Files	Coverage Δ	Complexity Δ
sql/src/main/java/io/crate/plugin/SQLPlugin.java	100% <ø> (ø)	15 <0> (?)

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[seut]

lgtm