code: @Override
      public <T> T onlyOne(Class<T> serviceClass, Class<? extends T> defaultServiceClass) {
          T one = null;
          try {
              one = onlyOne(serviceClass);
          } catch (Exception e) {
          }
  
          if (one == null) {
              one = createServiceInstance(defaultServiceClass);
          }
          return one;
      }
docs: /* (non-Javadoc)
  @see org.jboss.arquillian.core.spi.ServiceLoader#onlyOne(java.lang.Class, java.lang.Class)