code: @Override
      public void setProxyURL(final String url) throws RepositoryRuntimeException {
          try {
              getNode().setProperty(PROXY_FOR, url);
              // clear redirect property, in case it used to be a redirect
              getNode().setProperty(REDIRECTS_TO, (Value) null);
          } catch (final RepositoryException e) {
              throw new RepositoryRuntimeException(e);
          }
      }
docs: /*
  (non-Javadoc)
  @see org.fcrepo.kernel.api.models.FedoraBinary#setProxyURL()