Minor fix in FlowPartialViewContext

The fix ensures that getRenderIds returns a mutable collection as
stated in the contract for the method in PartialViewContext.

Issues: SWF-1480

spring-faces/src/test/java/org/springframework/faces/webflow/FlowPartialViewContextTests.java

@@ -16,6 +16,7 @@ import org.springframework.webflow.test.MockRequestContext;
 
 public class FlowPartialViewContextTests extends TestCase {
 
+	@SuppressWarnings("unchecked")
 	public void testReturnFragmentIds() throws Exception {
 		String[] fragmentIds = new String[] { "foo", "bar" };
 
@@ -46,4 +47,18 @@ public class FlowPartialViewContextTests extends TestCase {
 		assertEquals(renderIds, context.getRenderIds());
 	}
 
+	@SuppressWarnings("unchecked")
+	public void testReturnFragmentIdsMutable() throws Exception {
+		String[] fragmentIds = new String[] { "foo", "bar" };
+
+		RequestContext requestContext = new MockRequestContext();
+		requestContext.getFlashScope().asMap().put(View.RENDER_FRAGMENTS_ATTRIBUTE, fragmentIds);
+		RequestContextHolder.setRequestContext(requestContext);
+
+		Collection<String> renderIds = new FlowPartialViewContext(null).getRenderIds();
+		renderIds.add("baz");
+
+		assertEquals(Arrays.asList("foo", "bar", "baz"), renderIds);
+	}
+
 }