If you ever face issues like
BINDING.JCA-12563 Exception occurred when binding was invoked. Exception occurred during invocation of JCA binding: “JCA Binding execute of Reference operation ‘Write’ failed due to: Input Source null. Input Source null. Input Source is null. “. The invoked JCA adapter raised a resource exception. Please examine the above error message carefully to determine a resolution.
then there is a problem in the xml transformation in the mediator to write the file
Look if the transformation information in the mediator is proper.
Check if the transformation exist in the first place.