more postgresql type fixes

internal/tasks/monthlyAggregate.go

@@ -769,12 +769,12 @@ WHERE "Date" >= %d AND "Date" < %d
 func buildCanonicalDailyRollupSummaryUnion(start, end time.Time) string {
 	return fmt.Sprintf(`
 SELECT
-  NULL AS "InventoryId",
+  CAST(NULL AS BIGINT) AS "InventoryId",
   COALESCE("Name",'') AS "Name",
   COALESCE("Vcenter",'') AS "Vcenter",
   COALESCE("VmId",'') AS "VmId",
-  NULL AS "EventKey",
-  NULL AS "CloudId",
+  CAST(NULL AS TEXT) AS "EventKey",
+  CAST(NULL AS TEXT) AS "CloudId",
   COALESCE("CreationTime",0) AS "CreationTime",
   COALESCE("DeletionTime",0) AS "DeletionTime",
   COALESCE("LastResourcePool",'') AS "ResourcePool",