public static void checkProxyPortProperty() throws NumberFormatException {
    checkNumericSystemProperty("http.proxyPort", Range.closed(0, 65535));
    checkNumericSystemProperty("https.proxyPort", Range.closed(0, 65535));
  }
Checks if {@code http.proxyPort} and {@code https.proxyPort} system properties are in the
[0..65535] range when set.

@throws NumberFormatException if invalid values
jib-core/src/main/java/com/google/cloud/tools/jib/global/JibSystemProperties.java