RecordFieldSetMapper shouldn't reject null values

Close GH-5392

Signed-off-by: Yanming Zhou <zhouyanming@gmail.com>

Author: quaff

spring-batch-infrastructure/src/main/java/org/springframework/batch/infrastructure/item/file/mapping/RecordFieldSetMapper.java

@@ -33,6 +33,7 @@
  * @param <T> type of mapped items
  * @author Mahmoud Ben Hassine
  * @author Seungyong Hong
+ * @author Yanming Zhou
  * @since 4.3
  */
 public class RecordFieldSetMapper<T> implements FieldSetMapper<T> {
@@ -76,14 +77,12 @@ public T mapFieldSet(FieldSet fieldSet) {
 		Assert.isTrue(fieldSet.getFieldCount() == this.constructorParameterNames.length,
 				"Fields count must be equal to record components count");
 		Assert.isTrue(fieldSet.hasNames(), "Field names must be specified");
-		Object[] args = new Object[this.constructorParameterNames.length];
+		@Nullable Object[] args = new Object[this.constructorParameterNames.length];
 		for (int i = 0; i < args.length; i++) {
 			String name = this.constructorParameterNames[i];
 			Class<?> type = this.constructorParameterTypes[i];
 			Assert.notNull(name, "Constructor parameter names must not be null");
 			Object converted = this.typeConverter.convertIfNecessary(fieldSet.readRawString(name), type);
-			Assert.notNull(converted,
-					() -> String.format("Cannot convert field '%s' to required type '%s'", name, type.getName()));
 			args[i] = converted;
 		}
 		return BeanUtils.instantiateClass(this.mappedConstructor, args);

spring-batch-infrastructure/src/test/java/org/springframework/batch/infrastructure/item/file/mapping/RecordFieldSetMapperTests.java

@@ -17,17 +17,18 @@
 
 import org.junit.jupiter.api.Test;
 
-import org.springframework.batch.infrastructure.item.file.mapping.RecordFieldSetMapper;
 import org.springframework.batch.infrastructure.item.file.transform.DefaultFieldSet;
 import org.springframework.batch.infrastructure.item.file.transform.FieldSet;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
 /**
  * @author Mahmoud Ben Hassine
  * @author Seungyong Hong
+ * @author Yanming Zhou
  */
 class RecordFieldSetMapperTests {
 
@@ -83,10 +84,25 @@ void testMapFieldSetWhenEmptyRecord() {
 		assertNotNull(empty);
 	}
 
+	@Test
+	void testMapFieldSetWhenFieldsMayBeNull() {
+		// given
+		RecordFieldSetMapper<User> recordFieldSetMapper = new RecordFieldSetMapper<>(User.class);
+		FieldSet fieldSet = new DefaultFieldSet(new String[] { "", "foo" }, new String[] { "id", "name" });
+
+		// when
+		User user = recordFieldSetMapper.mapFieldSet(fieldSet);
+		assertNotNull(user);
+		assertNull(user.id());
+	}
+
 	record Person(int id, String name) {
 	}
 
 	record EmptyRecord() {
 	}
 
+	record User(Integer id, String name) {
+	}
+
 }