XStreamGae JUnit Test Stack Trace

com.thoughtworks.xstream.converters.ConversionException: Cannot construct com.mycompany.myapp.Car as it does not have a no-args constructor : Cannot construct com.mycompany.myapp.Car as it does not have a no-args constructor
---- Debugging information ----
message             : Cannot construct com.mycompany.myapp.Car as it does not have a no-args constructor
cause-exception     : com.thoughtworks.xstream.converters.reflection.ObjectAccessException
cause-message       : Cannot construct com.mycompany.myapp.Car as it does not have a no-args constructor
class               : com.mycompany.myapp.Car
required-type       : com.mycompany.myapp.Car
converter-type      : com.thoughtworks.xstream.converters.reflection.ReflectionConverter
path                : /com.mycompany.myapp.Car
line number         : 1
version             : null
-------------------------------
	at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:79)
	at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:65)
	at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:66)
	at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:50)
	at com.thoughtworks.xstream.core.TreeUnmarshaller.start(TreeUnmarshaller.java:134)
	at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.unmarshal(AbstractTreeMarshallingStrategy.java:32)
	at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1052)
	at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1036)
	at com.thoughtworks.xstream.XStream.fromXML(XStream.java:912)
	at com.thoughtworks.xstream.XStream.fromXML(XStream.java:903)
	at com.mycompany.myapp.XStreamGaeTest.testStringKeys(XStreamGaeTest.java:34)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:601)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:30)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
	at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
	at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: com.thoughtworks.xstream.converters.reflection.ObjectAccessException: Cannot construct com.mycompany.myapp.Car as it does not have a no-args constructor
	at com.thoughtworks.xstream.converters.reflection.PureJavaReflectionProvider.newInstance(PureJavaReflectionProvider.java:71)
	at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.instantiateNewInstance(AbstractReflectionConverter.java:428)
	at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.unmarshal(AbstractReflectionConverter.java:233)
	at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:72)
	... 35 more