code: public T withCatalog(IonCatalog catalog)
      {
          T b = mutable();
          b.setCatalog(catalog);
          return b;
      }
docs: Declares the catalog to use when building an {@link IonWriter},
  returning a new mutable builder if this is immutable.
  
  @param catalog the catalog to use in built writers.
  If null, the writer will be unable to resolve manually-written imports
  and may throw an exception.
  
  @return this instance, if mutable;
  otherwise a mutable copy of this instance.
  
  @see #getCatalog()
  @see #setCatalog(IonCatalog)