RESOLVED - BATCH-900: Retreive null values from the ExecutionContext

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/ExecutionContext.java

@@ -34,6 +34,14 @@ import org.springframework.util.Assert;
  */
 public class ExecutionContext implements Serializable {
 
+	/**
+	 * Underlying {@link ConcurrentHashMap} does not accept <code>null</code>
+	 * values, so we convert it to a private constant under the covers.
+	 */
+	private static enum Constants {
+		NULL
+	};
+
 	private volatile boolean dirty = false;
 
 	private final Map<String, Object> map;
@@ -112,6 +120,9 @@ public class ExecutionContext implements Serializable {
 		if (value != null) {
 			Assert.isInstanceOf(Serializable.class, value, "Value: [ " + value + "must be serializable.");
 		}
+		else {
+			value = Constants.NULL;
+		}
 		dirty = true;
 		map.put(key, value);
 	}
@@ -233,6 +244,10 @@ public class ExecutionContext implements Serializable {
 
 		Object value = map.get(key);
 
+		if (value == Constants.NULL) {
+			return null;
+		}
+
 		if (!type.isInstance(value)) {
 			throw new ClassCastException("Value for key=[" + key + "] is not of type: [" + type + "], it is ["
 					+ (value == null ? null : "(" + value.getClass() + ")" + value) + "]");