Fix InsertBulkColumnDefinition NullNotNull marshaling

Always include NullNotNull field in JSON output, using "NotSpecified"
as the default value when empty or unspecified.

Enables BaselinesCommon_BulkInsertStatementTests test.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kyleconroy

parser/marshal.go

@@ -15707,9 +15707,12 @@ func insertBulkColumnDefinitionToJSON(c *ast.InsertBulkColumnDefinition) jsonNod
 	if c.Column != nil {
 		node["Column"] = columnDefinitionBaseToJSON(c.Column)
 	}
-	if c.NullNotNull != "" && c.NullNotNull != "Unspecified" {
-		node["NullNotNull"] = c.NullNotNull
+	// Always include NullNotNull - use "NotSpecified" if empty
+	nullNotNull := c.NullNotNull
+	if nullNotNull == "" || nullNotNull == "Unspecified" {
+		nullNotNull = "NotSpecified"
 	}
+	node["NullNotNull"] = nullNotNull
 	return node
 }
 

parser/testdata/BaselinesCommon_BulkInsertStatementTests/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}