fix(sql-lab): do not replace undefined schema with empty object (#19664)

superset-frontend/src/SqlLab/actions/sqlLab.js

@@ -791,7 +791,7 @@ export function queryEditorSetSchema(queryEditor, schema) {
         dispatch({
           type: QUERY_EDITOR_SET_SCHEMA,
           queryEditor: queryEditor || {},
-          schema: schema || {},
+          schema,
         }),
       )
       .catch(() =>

superset-frontend/src/SqlLab/types.ts

@@ -61,7 +61,7 @@ export type Query = {
     query: { limit: number };
   };
   resultsKey: string | null;
-  schema: string;
+  schema?: string;
   sql: string;
   sqlEditorId: string;
   state: QueryState;