code: public ModelNode getDeploymentSubModel(final String subsystemName, final PathElement address) {
          assert subsystemName != null : "The subsystemName cannot be null";
          return getDeploymentSubModel(subsystemName, address, deploymentUnit);
      }
docs: Gets the sub-model for a components from the deployment itself. Operations, metrics and descriptions have to be
  registered as part of the subsystem registration {@link org.jboss.as.controller.ExtensionContext} and
  {@link org.jboss.as.controller.SubsystemRegistration#registerDeploymentModel(org.jboss.as.controller.ResourceDefinition)}.
  
  <p>
  If the subsystem resource does not exist it will be created. If no resource exists for the address parameter on
  the resource it also be created.
  </p>
  
  @param subsystemName the name of the subsystem
  @param address       the path address this sub-model should return the model for
  
  @return the model for the resource