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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 get_cameras_signal_strength(self):
 """Return a list of signal strength of all cameras."""

        signal_strength = {}
        if not self.camera_properties:
            return None

        for camera in self.camera_properties:
            serialnum = camera.get('serialNumber')
            cam_strength = camera.get('signalStrength')
            signal_strength[serialnum] = cam_strength
        return signal_strength