Additional collation support for the NULLIF conditional expression has been added

## Feature Additional [collation support](https://cloud.google.com/bigquery/docs/reference/standard-sql/collation-concepts) for the [NULLIF conditional expression](https://cloud.google.com/bigquery/docs/reference/standard-sql/conditional%5Fexpressions#nullif) has been added. The `NULLIF` conditional expression is now affected by collation and can be used in collation-supported comparisons with the `STRUCT` data type. This feature is [generally available](https://cloud.google.com/products#product-launch-stages) (GA).