HHH-18069 NullPointerException when unioning partition results

Author: dreab8

hibernate-core/src/main/java/org/hibernate/query/sqm/sql/BaseSqmToSqlAstConverter.java

@@ -1982,9 +1982,13 @@ public QueryGroup visitQueryGroup(SqmQueryGroup<?> queryGroup) {
 		sqmQueryPartStack.push( queryGroup );
 		pushProcessingState( processingState );
 
+		FromClauseIndex firstQueryPartIndex = null;
+		SqlAstProcessingState firstPoppedProcessingState = null;
 		try {
 			newQueryParts.add( visitQueryPart( queryParts.get( 0 ) ) );
 
+			firstQueryPartIndex = lastPoppedFromClauseIndex;
+			firstPoppedProcessingState = lastPoppedProcessingState;
 			collector.setSqmAliasedNodeCollector(
 					(SqmAliasedNodeCollector) lastPoppedProcessingState.getSqlExpressionResolver()
 			);
@@ -2002,6 +2006,8 @@ public QueryGroup visitQueryGroup(SqmQueryGroup<?> queryGroup) {
 		finally {
 			popProcessingStateStack();
 			sqmQueryPartStack.pop();
+			lastPoppedFromClauseIndex = firstQueryPartIndex;
+			lastPoppedProcessingState = firstPoppedProcessingState;
 		}
 	}