special handling for literal null inside a cast in select clause

this caused a failure on Informix

Author: gavinking

hibernate-community-dialects/src/main/java/org/hibernate/community/dialect/InformixSqlAstTranslator.java

@@ -205,7 +205,7 @@ public void visitValuesTableReference(ValuesTableReference tableReference) {
 	protected boolean shouldEmulateFetchClause(QueryPart queryPart) {
 		// Check if current query part is already row numbering to avoid infinite recursion
 		return useOffsetFetchClause( queryPart ) && getQueryPartForRowNumbering() != queryPart
-			   && getDialect().supportsWindowFunctions() && !isRowsOnlyFetchClauseType( queryPart );
+			&& getDialect().supportsWindowFunctions() && !isRowsOnlyFetchClauseType( queryPart );
 	}
 
 	@Override

hibernate-core/src/main/java/org/hibernate/dialect/function/CastFunction.java

@@ -77,6 +77,9 @@ public void render(
 			renderCastArrayToString( sqlAppender, arguments.get( 0 ), dialect, walker );
 		}
 		else {
+			if ( source instanceof QueryLiteral<?> literal && literal.getLiteralValue() == null ) {
+				literal.setInCast(true);
+			}
 			new PatternRenderer( dialect.castPattern( sourceType, targetType ) )
 					.render( sqlAppender, arguments, walker );
 		}

hibernate-core/src/main/java/org/hibernate/sql/ast/spi/AbstractSqlAstTranslator.java

@@ -7439,7 +7439,12 @@ public void visitJdbcLiteral(JdbcLiteral<?> jdbcLiteral) {
 
 	@Override
 	public void visitQueryLiteral(QueryLiteral<?> queryLiteral) {
-		visitLiteral( queryLiteral );
+		if ( queryLiteral.getLiteralValue() == null && queryLiteral.isInCast() ) {
+			appendSql( SqlAppender.NULL_KEYWORD );
+		}
+		else {
+			visitLiteral( queryLiteral );
+		}
 	}
 
 	@Override

hibernate-core/src/main/java/org/hibernate/sql/ast/tree/expression/QueryLiteral.java

@@ -30,6 +30,7 @@
 public class QueryLiteral<T> implements Literal, DomainResultProducer<T> {
 	private final T value;
 	private final SqlExpressible expressible;
+	private boolean inCast;
 
 	public QueryLiteral(T value, SqlExpressible expressible) {
 		assert value == null || expressible.getJdbcMapping().getJdbcJavaType().isInstance( value );
@@ -100,4 +101,12 @@ public void applySqlSelections(DomainResultCreationState creationState) {
 				creationState.getSqlAstCreationState().getCreationContext().getMappingMetamodel().getTypeConfiguration()
 		);
 	}
+
+	public void setInCast(boolean inCast) {
+		this.inCast = inCast;
+	}
+
+	public boolean isInCast() {
+		return inCast;
+	}
 }