There is no clean behaviour specified for javax.script.CompiledScript methods:
public Object eval()
public Object eval(Bindings nn)

The spec says only common words that compiled script should be executed.

So, if we have realized methods in abstract class it is reazonable to specify how they should work. Or they just should be abstract.

Other issue for "public Object eval(Bindings nn)" method:
The specs says nothing about case then specified Bindings is null. Should the method throw the NPE or not ? Looks like must because it is Bindings for ENGINE_SCOPE and the spec for ScriptContext.setBindings says that NPE is thrown in case of null Bindings for ENGINE_SCOPE scope.