feat(optimizer)!: bq annotate type for NULL

Author: geooo109

sqlglot/typing/bigquery.py

@@ -160,6 +160,7 @@ def _annotate_array(self: TypeAnnotator, expression: exp.Array) -> exp.Array:
             exp.LaxInt64,
             exp.Length,
             exp.Ntile,
+            exp.Null,
             exp.Rank,
             exp.RangeBucket,
             exp.RegexpInstr,

tests/fixtures/optimizer/annotate_types.sql

@@ -122,3 +122,7 @@ DATETIME;
 # dialect: bigquery
 CASE WHEN TRUE THEN TIMESTAMP '2020-02-02 00:00:00' ELSE '2010-01-01' END;
 TIMESTAMP;
+
+# dialect: bigquery
+NULL;
+BIGINT;