code: @Nonnull
      public Descriptor getDescriptorOrDie(Class<? extends Describable> type) {
          Descriptor d = getDescriptor(type);
          if (d==null)
              throw new AssertionError(type+" is missing its descriptor");
          return d;
      }
docs: Works just like {@link #getDescriptor(Class)} but don't take no for an answer.
  
  @throws AssertionError
  If the descriptor is missing.
  @since 1.326