Add nullCoder on Record and Disjunction coders

[regadas]

No description provided.

[codecov]

Codecov Report

Merging #3349 into master will decrease coverage by 2.54%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3349      +/-   ##
==========================================
- Coverage   72.70%   70.15%   -2.55%     
==========================================
  Files         234      234              
  Lines        7708     7710       +2     
  Branches      333      348      +15     
==========================================
- Hits         5604     5409     -195     
- Misses       2104     2301     +197     

Impacted Files	Coverage Δ
...la/com/spotify/scio/coders/CoderMaterializer.scala	100.00% <100.00%> (ø)
...scala/com/spotify/scio/bigquery/client/Cache.scala	0.00% <0.00%> (-74.08%)	⬇️
.../spotify/scio/bigquery/client/BigQueryConfig.scala	0.00% <0.00%> (-70.59%)	⬇️
.../spotify/scio/bigquery/BigQueryPartitionUtil.scala	0.00% <0.00%> (-52.50%)	⬇️
...scala/com/spotify/scio/bigquery/BigQueryUtil.scala	50.00% <0.00%> (-50.00%)	⬇️
...otify/scio/bigquery/syntax/ScioContextSyntax.scala	21.87% <0.00%> (-40.63%)	⬇️
...la/com/spotify/scio/bigquery/client/QueryOps.scala	0.73% <0.00%> (-39.71%)	⬇️
.../scala/com/spotify/scio/bigquery/StorageUtil.scala	0.00% <0.00%> (-36.85%)	⬇️
...com/spotify/scio/bigquery/types/BigQueryType.scala	58.33% <0.00%> (-29.17%)	⬇️
...la/com/spotify/scio/bigquery/client/TableOps.scala	0.00% <0.00%> (-25.00%)	⬇️
... and 3 more

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