Fix prevent dirty flag from being set to false when pushing null

Author: GGHDMS

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

@@ -133,7 +133,10 @@ public void put(String key, @Nullable Object value) {
 		}
 		else {
 			Object result = this.map.remove(key);
-			this.dirty = result != null;
+
+			if (!this.dirty) {
+				this.dirty = result != null;
+			}
 		}
 	}
 

spring-batch-infrastructure/src/test/java/org/springframework/batch/item/ExecutionContextTests.java

@@ -88,11 +88,13 @@ void testNotDirtyWithDuplicate() {
 	}
 
 	@Test
-	void testNotDirtyWithRemoveMissing() {
+	void testDirtyWithRemoveMissing() {
 		context.putString("1", "test");
 		assertTrue(context.isDirty());
 		context.putString("1", null); // remove an item that was present
 		assertTrue(context.isDirty());
+
+		context.clearDirtyFlag();
 		context.putString("1", null); // remove a non-existent item
 		assertFalse(context.isDirty());
 	}