code: public boolean hasDeploymentSubModel(final String subsystemName, final PathElement address) {
          final Resource root = deploymentUnit.getAttachment(DEPLOYMENT_RESOURCE);
          final PathElement subsystem = PathElement.pathElement(SUBSYSTEM, subsystemName);
          return root.hasChild(subsystem) && (address == null || root.getChild(subsystem).hasChild(address));
      }
docs: Checks to see if a resource has already been registered for the specified address on the subsystem.
  
  @param subsystemName the name of the subsystem
  @param address       the address to check
  
  @return {@code true} if the address exists on the subsystem otherwise {@code false}