Fix an NPE in TaskDataState

Change-Id: Ibcbe27570fcc2f49a0b8e92cf47db0eeedbab0f2
(cherry picked from commit 5a6fd14e29e39048c4421e89d0d760938da4e398)
diff --git a/org.eclipse.mylyn.tasks.core/src/org/eclipse/mylyn/internal/tasks/core/data/TaskDataState.java b/org.eclipse.mylyn.tasks.core/src/org/eclipse/mylyn/internal/tasks/core/data/TaskDataState.java
index 9cca8ae..ee39a1b 100644
--- a/org.eclipse.mylyn.tasks.core/src/org/eclipse/mylyn/internal/tasks/core/data/TaskDataState.java
+++ b/org.eclipse.mylyn.tasks.core/src/org/eclipse/mylyn/internal/tasks/core/data/TaskDataState.java
@@ -221,6 +221,9 @@
 	}
 
 	public static TaskData createCopy(TaskData oldData) {
+		if (oldData == null) {
+			return null;
+		}
 		return createCopy(oldData, oldData.getTaskId());
 	}