code: def validate_input(self):
          
          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
docs: 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