code: private static ApplicationEngine findDelegate() {
  		try {
  			ApplicationEngine result=createApplicationEngineFromSPI();
  			if(result==null) {
  				result=createApplicationEngineFromConfigurationFile();
  			}
  
  			if(result==null) {
  				final String delegateClassName = System.getProperty(LDP4J_APPLICATION_ENGINE_PROPERTY);
  				if(delegateClassName!=null) {
  					result=createApplicationEngineForClassName(delegateClassName);
  				}
  			}
  
  			return result;
  		} catch (final Exception ex) {
  			throw new IllegalStateException("Could not find application engine",ex);
  		}
  	}
docs: Obtain an {@code ApplicationEngine} instance using the method described
  in {@link ApplicationEngine#engine()}.
  
  @return an instance of {@code ApplicationEngine} if available, or null if
  a default implementation class is to be selected.