MockViewFactoryCreator not backwards compatible with Java 1.4

There is a call to a method that was only added in java 1.5 within one of the Mock classes used when testing xml flows. The particular call causing problems is

context.getExternalContext().getResponseWriter().append(viewId);

of

org.springframework.webflow.test.MockViewFactoryCreator$MockView.render(MockViewFactoryCreator.java:109)

The method append was only added to the Writer class as of 1.5, therefore when using java 1.4 then following NoSuchMethodError occurs, I have worked round this for the time being by running the test with the 1.5 runtime, but this is not ideal.

java.lang.NoSuchMethodError: java.io.Writer.append(Ljava/lang/CharSequence;)Ljava/io/Writer;
at org.springframework.webflow.test.MockViewFactoryCreator$MockView.render(MockViewFactoryCreator.java:109)
at org.springframework.webflow.engine.ViewState.render(ViewState.java:240)
at org.springframework.webflow.engine.ViewState.doEnter(ViewState.java:179)
at org.springframework.webflow.engine.State.enter(State.java:193)
at org.springframework.webflow.engine.Transition.execute(Transition.java:222)
at org.springframework.webflow.engine.DecisionState.doEnter(DecisionState.java:51)
at org.springframework.webflow.engine.State.enter(State.java:193)
at org.springframework.webflow.engine.Flow.start(Flow.java:515)
at org.springframework.webflow.engine.impl.FlowExecutionImpl.start(FlowExecutionImpl.java:357)
at org.springframework.webflow.engine.impl.FlowExecutionImpl.start(FlowExecutionImpl.java:239)
at org.springframework.webflow.test.execution.AbstractFlowExecutionTests.startFlow(AbstractFlowExecutionTests.java:123)
at org.springframework.webflow.test.execution.AbstractFlowExecutionTests.startFlow(AbstractFlowExecutionTests.java:111)