Fix NPE in JobParameters.toProperties on null parameter value

Issue #834

Author: acktsap

spring-batch-core/src/main/java/org/springframework/batch/core/JobParameters.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2018 the original author or authors.
+ * Copyright 2006-2021 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.
@@ -20,6 +20,7 @@
 import java.util.Date;
 import java.util.LinkedHashMap;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Properties;
 
 import org.springframework.lang.Nullable;
@@ -38,6 +39,7 @@
  * @author Lucas Ward
  * @author Michael Minella
  * @author Mahmoud Ben Hassine
+ * @author Taeik Lim
  * @since 1.0
  */
 @SuppressWarnings("serial")
@@ -269,8 +271,8 @@ public Properties toProperties() {
 		Properties props = new Properties();
 
 		for (Map.Entry<String, JobParameter> param : parameters.entrySet()) {
-			if(param.getValue() != null) {
-				props.put(param.getKey(), param.getValue().toString());
+			if (param.getValue() != null) {
+				props.put(param.getKey(), Objects.toString(param.getValue().toString(), ""));
 			}
 		}
 

spring-batch-core/src/test/java/org/springframework/batch/core/JobParametersTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2008-2018 the original author or authors.
+ * Copyright 2008-2021 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.
@@ -25,6 +25,7 @@
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.Properties;
 
 import org.junit.Before;
 import org.junit.Test;
@@ -35,6 +36,7 @@
  * @author Dave Syer
  * @author Michael Minella
  * @author Mahmoud Ben Hassine
+ * @author Taeik Lim
  *
  */
 public class JobParametersTests {
@@ -228,4 +230,15 @@ public void testDoubleReturnsNullWhenKeyDoesntExit(){
 	public void testDateReturnsNullWhenKeyDoesntExit(){
 		assertNull(new JobParameters().getDate("keythatdoesntexist"));
 	}
+
+	@Test
+	public void testToPropertiesWithNullValue() {
+		Map<String, JobParameter> parameterMap = new HashMap<>();
+		Long value = null;
+		parameterMap.put("nullkey", new JobParameter(value));
+		JobParameters jobParameters = new JobParameters(parameterMap);
+
+		Properties properties = jobParameters.toProperties();
+		assertEquals("", properties.get("nullkey"));
+	}
 }