Fix lambda nullability in JdbcOperations extensions

Closes gh-22682

Author: sdeleuze

spring-jdbc/src/main/kotlin/org/springframework/jdbc/core/JdbcOperationsExtensions.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors
+ * Copyright 2002-2019 the original author or authors
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -34,7 +34,7 @@ inline fun <reified T : Any> JdbcOperations.queryForObject(sql: String): T? =
  * @author Mario Arias
  * @since 5.0
  */
-fun <T : Any> JdbcOperations.queryForObject(sql: String, vararg args: Any, function: (ResultSet, Int) -> T): T? =
+fun <T : Any?> JdbcOperations.queryForObject(sql: String, vararg args: Any, function: (ResultSet, Int) -> T): T? =
 		queryForObject(sql, RowMapper { resultSet, i -> function(resultSet, i) }, *args)
 
 /**
@@ -96,7 +96,7 @@ inline fun <reified T : Any> JdbcOperations.queryForList(sql: String, args: Arra
  * @author Mario Arias
  * @since 5.0
  */
-inline fun <reified T : Any> JdbcOperations.query(sql: String, vararg args: Any,
+inline fun <reified T : Any?> JdbcOperations.query(sql: String, vararg args: Any,
 		crossinline function: (ResultSet) -> T): T? =
 		query(sql, ResultSetExtractor { function(it) }, *args)
 

spring-jdbc/src/test/kotlin/org/springframework/jdbc/core/JdbcOperationsExtensionsTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors
+ * Copyright 2002-2019 the original author or authors
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -51,6 +51,13 @@ class JdbcOperationsExtensionsTests {
 		verify(template, times(1)).queryForObject(eq(sql), any<RowMapper<Int>>(), eq(3))
 	}
 
+	@Test  // gh-22682
+	fun `queryForObject with nullable RowMapper-like function`() {
+		val sql = "select age from customer where id = ?"
+		template.queryForObject(sql, 3) { _, _ -> null as Int? }
+		verify(template, times(1)).queryForObject(eq(sql), any<RowMapper<Int?>>(), eq(3))
+	}
+
 	@Test
 	fun `queryForObject with reified type parameters and argTypes`() {
 		val sql = "select age from customer where id = ?"
@@ -102,6 +109,13 @@ class JdbcOperationsExtensionsTests {
 		verify(template, times(1)).query(eq(sql), any<ResultSetExtractor<Int>>(), eq(3))
 	}
 
+	@Test  // gh-22682
+	fun `query with nullable ResultSetExtractor-like function`() {
+		val sql = "select age from customer where id = ?"
+		template.query<Int?>(sql, 3) { _ -> null }
+		verify(template, times(1)).query(eq(sql), any<ResultSetExtractor<Int?>>(), eq(3))
+	}
+
 	@Test
 	fun `query with RowCallbackHandler-like function`() {
 		val sql = "select age from customer where id = ?"