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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def process(self, rpc_executor, mark_streamer=None):
 """Run this node's processing function. Args: rpc_executor (RPCExecutor):
 An object capable of executing RPCs in case we need to do that. mark_streamer (callable):
 Function that can be called to manually mark a streamer as triggered by index. Returns: list(IOTileReading):
 A list of IOTileReadings with the results of the processing function or an empty list if no results were produced """


        if self.func is None:
            raise ProcessingFunctionError('No processing function set for node', stream=self.stream)

        results = self.func(*[x[0] for x in self.inputs], rpc_executor=rpc_executor, mark_streamer=mark_streamer)
        if results is None:
            results = []

        return results