public void setProxyIp(String proxyIp) {
        this.proxyIp = proxyIp == null ? Pac4jConstants.EMPTY_STRING : proxyIp;
    }
<p>Setter for the field <code>proxyIp</code>.</p>

@param proxyIp Set the IP to verify the proxy request source.
              Setting {@code null} or {@code ""} (empty string) disabled the proxy IP check.
pac4j-http/src/main/java/org/pac4j/http/credentials/extractor/IpExtractor.java