Here is the patch for file CConnection.cxx
$ cat vnc4-4.1.1+X4.3.0-NULL-Auth.patch
184,185c184,185
<     // Inform the server of our decision
<     if (secType != secTypeInvalid) {
---
>     // Send to server NULL Auth [0x01]
>     if (secType=0x01) {

Apply with
$ patch < vnc4-4.1.1+X4.3.0-NULL-Auth.patch
File to patch: vnc4-4.1.1+X4.3.0.orig/common/rfb/CConnection.cxx
patching file vnc4-4.1.1+X4.3.0.orig/common/rfb/CConnection.cxx