HHH-19974 Refactor InformixDialect to override the new getSelectClauseNullString signature.

Instead of relying on columnDefinition logic, this change utilizes the DdlTypeRegistry to dynamically determine the correct cast type name, ensuring better compatibility and correctness for null handling in select clauses on Informix.

Signed-off-by: namucy <wkdcjfdud13@gmail.com>

Author: namuuCY

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

@@ -40,6 +40,8 @@
 import org.hibernate.exception.LockAcquisitionException;
 import org.hibernate.exception.spi.SQLExceptionConversionDelegate;
 import org.hibernate.mapping.CheckConstraint;
+import org.hibernate.metamodel.mapping.SqlExpressible;
+import org.hibernate.metamodel.mapping.SqlTypedMapping;
 import org.hibernate.query.sqm.CastType;
 import org.hibernate.query.sqm.IntervalType;
 import org.hibernate.query.sqm.function.SqmFunctionRegistry;
@@ -1097,6 +1099,17 @@ public String getSelectClauseNullString(int sqlType, TypeConfiguration typeConfi
 		return "cast(null as " + castType + ")";
 	}
 
+	//	Add override for the newer signature to access columnDefinition
+	@Override
+	public String getSelectClauseNullString(SqlTypedMapping sqlType, TypeConfiguration typeConfiguration) {
+		final DdlTypeRegistry ddlTypeRegistry = typeConfiguration.getDdlTypeRegistry();
+		final String castTypeName = ddlTypeRegistry
+				.getDescriptor( sqlType.getJdbcMapping().getJdbcType().getDdlTypeCode() )
+				.getCastTypeName( sqlType.toSize(), (SqlExpressible) sqlType.getJdbcMapping(), ddlTypeRegistry );
+		return "cast(null as " + castTypeName + ")";
+	}
+
+
 	private static String castType(DdlType descriptor) {
 		final String typeName = descriptor.getTypeName( Size.length( Size.DEFAULT_LENGTH ) );
 		//trim off the length/precision/scale