code: public final void setAllowedReferers(@Nullable final List<? extends URIMatcher> matchers) {
          this.allowedReferers = matchers != null ? new UriMatchers(matchers) : null;
      }
docs: The matchers used to authorize the incoming requests in function of the referer. For example:
  <pre><code>
  allowedReferers:
  - !hostnameMatch
  host: example.com
  allowSubDomains: true
  </code></pre>
  <p>
  By default, the referer is not checked
  
  @param matchers the list of matcher to use to check if a referer is permitted or null for no
  check
  @see org.mapfish.print.processor.http.matcher.URIMatcher