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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 validate_input(self):
 """Validate the input before saving a scenario. Those validations are: 1. self.exposure_layer must be not None 2. self.hazard_layer must be not None 3. self.function_id is not an empty string or None """

        self.exposure_layer = layer_from_combo(self.dock.exposure_layer_combo)
        self.hazard_layer = layer_from_combo(self.dock.hazard_layer_combo)
        self.aggregation_layer = layer_from_combo(
            self.dock.aggregation_layer_combo)

        is_valid = True
        warning_message = None
        if self.exposure_layer is None:
            warning_message = tr(
                'Exposure layer is not found, can not save scenario. Please '
                'add exposure layer to do so.')
            is_valid = False

        if self.hazard_layer is None:
            warning_message = tr(
                'Hazard layer is not found, can not save scenario. Please add '
                'hazard layer to do so.')
            is_valid = False

        return is_valid, warning_message