Fix null column index issue during dbt docs generate for external t…

…ables (#1085)

* coalesce column metadata columns with a value to avoid null errors for external tables in docs generate

* changelog

.changes/unreleased/Fixes-20240201-145323.yaml

@@ -0,0 +1,6 @@
+kind: Fixes
+body: Fix null column index issue during `dbt docs generate` for external tables
+time: 2024-02-01T14:53:23.434624-05:00
+custom:
+  Author: mikealfare
+  Issue: "1079"

dbt/include/bigquery/macros/catalog/catalog.sql

@@ -121,10 +121,12 @@
         end as table_name,
         tables.table_type,
         tables.table_comment,
-        columns.column_name,
-        columns.column_index,
-        columns.column_type,
-        columns.column_comment,
+        -- coalesce column metadata fields to ensure they are non-null for catalog generation
+        -- external table columns are not present in COLUMN_FIELD_PATHS
+        coalesce(columns.column_name, '<unknown>') as column_name,
+        coalesce(columns.column_index, 1) as column_index,
+        coalesce(columns.column_type, '<unknown>') as column_type,
+        coalesce(columns.column_comment, '') as column_comment,
 
         'Shard count' as `stats__date_shards__label`,
         table_stats.shard_count as `stats__date_shards__value`,