HHH-17677 handle literal null arguments more elegantly in StandardFunctionReturnTypeResolvers

resolves a very confusing error message

Author: gavinking

hibernate-core/src/main/java/org/hibernate/query/sqm/produce/function/StandardFunctionReturnTypeResolvers.java

@@ -12,16 +12,15 @@
 import java.util.function.Supplier;
 
 import org.hibernate.Internal;
-import org.hibernate.QueryException;
 import org.hibernate.metamodel.mapping.BasicValuedMapping;
 import org.hibernate.metamodel.mapping.JdbcMapping;
 import org.hibernate.metamodel.mapping.JdbcMappingContainer;
 import org.hibernate.metamodel.mapping.MappingModelExpressible;
-import org.hibernate.metamodel.model.domain.EntityDomainType;
 import org.hibernate.query.ReturnableType;
 import org.hibernate.query.sqm.SqmExpressible;
 import org.hibernate.query.sqm.SqmPathSource;
 import org.hibernate.query.sqm.tree.SqmTypedNode;
+import org.hibernate.query.sqm.tree.expression.NullSqmExpressible;
 import org.hibernate.sql.ast.tree.SqlAstNode;
 import org.hibernate.sql.ast.tree.expression.Expression;
 import org.hibernate.type.BasicType;
@@ -252,7 +251,10 @@ public static ReturnableType<?> extractArgumentType(
 			int position) {
 		final SqmTypedNode<?> specifiedArgument = arguments.get( position - 1 );
 		final SqmExpressible<?> specifiedArgType = getArgumentExpressible( specifiedArgument );
-		if ( specifiedArgType != null && !(specifiedArgType instanceof ReturnableType ) ) {
+		if ( specifiedArgType == null || specifiedArgType instanceof NullSqmExpressible ) {
+			return null;
+		}
+		else if ( !(specifiedArgType instanceof ReturnableType) ) {
 			throw new FunctionArgumentException(
 					String.format(
 							Locale.ROOT,
@@ -263,18 +265,19 @@ public static ReturnableType<?> extractArgumentType(
 					)
 			);
 		}
-
-		return (ReturnableType<?>) specifiedArgType;
+		else {
+			return (ReturnableType<?>) specifiedArgType;
+		}
 	}
 
 	private static SqmExpressible<?> getArgumentExpressible(SqmTypedNode<?> specifiedArgument) {
 		final SqmExpressible<?> expressible = specifiedArgument.getNodeType();
 		final SqmExpressible<?> specifiedArgType = expressible instanceof SqmTypedNode<?>
 				? ( (SqmTypedNode<?>) expressible ).getNodeType()
 				: expressible;
-		return specifiedArgType instanceof SqmPathSource ?
-				( (SqmPathSource<?>) specifiedArgType ).getSqmPathType() :
-				specifiedArgType;
+		return specifiedArgType instanceof SqmPathSource
+				? ( (SqmPathSource<?>) specifiedArgType ).getSqmPathType()
+				: specifiedArgType;
 	}
 
 	public static JdbcMapping extractArgumentJdbcMapping(

hibernate-core/src/main/java/org/hibernate/sql/results/internal/SqlSelectionImpl.java

@@ -11,7 +11,6 @@
 import org.hibernate.engine.spi.SessionFactoryImplementor;
 import org.hibernate.metamodel.mapping.JdbcMapping;
 import org.hibernate.metamodel.mapping.JdbcMappingContainer;
-import org.hibernate.metamodel.mapping.SqlExpressible;
 import org.hibernate.sql.ast.SqlAstWalker;
 import org.hibernate.sql.ast.spi.SqlExpressionAccess;
 import org.hibernate.sql.ast.spi.SqlSelection;
@@ -93,7 +92,10 @@ protected SqlSelectionImpl(
 	}
 
 	private static ValueExtractor determineValueExtractor(Expression sqlExpression, JavaType<?> jdbcJavaType) {
-		final JdbcMapping jdbcMapping = sqlExpression.getExpressionType().getSingleJdbcMapping();
+		final JdbcMappingContainer expressionType = sqlExpression.getExpressionType();
+		final JdbcMapping jdbcMapping = expressionType == null
+				? JavaObjectType.INSTANCE
+				: expressionType.getSingleJdbcMapping();
 		if ( jdbcJavaType == null || jdbcMapping.getMappedJavaType() == jdbcJavaType ) {
 			return jdbcMapping.getJdbcValueExtractor();
 		}
@@ -102,6 +104,7 @@ private static ValueExtractor determineValueExtractor(Expression sqlExpression,
 		}
 	}
 
+
 	@Override
 	public Expression getExpression() {
 		return sqlExpression;

hibernate-core/src/test/java/org/hibernate/orm/test/query/hql/FunctionTests.java

@@ -2248,4 +2248,22 @@ public void testTupleInSelect(SessionFactoryScope scope) {
 				}
 		);
 	}
+
+	@Test
+	@SkipForDialect(dialectClass = H2Dialect.class)
+	@SkipForDialect(dialectClass = DerbyDialect.class)
+	@SkipForDialect(dialectClass = HSQLDialect.class)
+	@SkipForDialect(dialectClass = DB2Dialect.class)
+	public void testNullInCoalesce(SessionFactoryScope scope) {
+		scope.inTransaction(s -> {
+			assertEquals("hello",
+					s.createQuery("select coalesce(null, :word)", String.class)
+							.setParameter("word", "hello")
+							.getSingleResultOrNull());
+			assertEquals("hello",
+					s.createQuery("select coalesce(:word, null)", String.class)
+							.setParameter("word", "hello")
+							.getSingleResultOrNull());
+        });
+	}
 }