Callback after a given method successfully returned.
returnValue - the value returned by the method, if any
method - the method being invoked
args - the arguments to the method
target - the target of the method invocation. May be null.
Throwable - if this object wishes to abort the call.
Any exception thrown will be returned to the caller if it's
allowed by the method signature. Otherwise the exception
will be wrapped as a runtime exception.