VerifyError on += of instance variable

class MyClass
{
count = 0;

doit()

}

o = new MyClass();
println "instantiated"
o.doit();
println o.count;

-----------
results in:
-----------

Exception in thread "main" java.lang.VerifyError: (class: MyClass, method: doit signature: ()Ljava/lang/Object Unable to pop operand off an empty stack
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at test2.class$(test2.gr)
at test2.run(test2.gr:14)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.codehaus.groovy.runtime.ReflectionMetaMethod.invoke(ReflectionMetaMethod.java:56)
at groovy.lang.MetaClass.doMethodInvoke(MetaClass.java:977)
at groovy.lang.MetaClass.invokeMethod(MetaClass.java:285)
at groovy.lang.MetaClass.invokeMethod(MetaClass.java:262)
at groovy.lang.GroovyObjectSupport.invokeMethod(GroovyObjectSupport.java:73)

...