code: private void addFingerprintAttribute(Text attribute) throws IllegalArgumentException {
      	if (!attribute.startsWith(SessionDescription.WEBRTC_FINGERPRINT)) {
      		throw new IllegalArgumentException("Not a valid fingerprint attribute"+attribute);
      	}
  
      	// Remove line type 'a=fingerprint:'
      	Text fingerprint = (Text) attribute.subSequence(SessionDescription.WEBRTC_FINGERPRINT.length(),attribute.length());
      	setWebRTCFingerprint(fingerprint);
      }
docs: Register a new fingerprint attribute for WebRTC calls.<br>
  Example: <code>a=fingerprint:sha-256 E5:52:E5:88:CC:B6:7A:D7:8E:...</code>
  
  @param attribute
  The attribute line to be registered.
  @throws IllegalArgumentException
  If the attribute is not a valid FMT line.