title: UnboundID LDAP DIGEST-MD5 binding cause NPE
body: <p>I'm getting the following error when I try to bind using DIGEST-MD5 against ApacheDS using UnboundID LDAP SDK.  I already tested the connection using simple bind with UnboundID and Apache Shiro so the ApacheDS is working.</p>
  
  <pre><code>LDAPException(resultCode=82 (local error), errorMessage='Unable to create a subsequent DIGEST-MD5 SASL request:  NullPointerException(trace='processChallenge(DigestMD5Client.java:339) / evaluateChallenge(DigestMD5Client.java:207) / processSASLBind(SASLHelper.java:149) / process(DIGESTMD5BindRequest.java:406) / bind(LDAPConnection.java:1837) / main(UnboundDemo.java:38)', revision=15579)')
      at com.unboundid.ldap.sdk.SASLHelper.processSASLBind(SASLHelper.java:154)
      at com.unboundid.ldap.sdk.DIGESTMD5BindRequest.process(DIGESTMD5BindRequest.java:406)
      at com.unboundid.ldap.sdk.LDAPConnection.bind(LDAPConnection.java:1837)
      at com.mizar.ldap.UnboundDemo.main(UnboundDemo.java:38)
  Caused by: java.lang.NullPointerException
      at com.sun.security.sasl.digest.DigestMD5Client.processChallenge(DigestMD5Client.java:339)
      at com.sun.security.sasl.digest.DigestMD5Client.evaluateChallenge(DigestMD5Client.java:207)
      at com.unboundid.ldap.sdk.SASLHelper.processSASLBind(SASLHelper.java:149)
      ... 3 more
  </code></pre>
  
  <p>I followed the example in the JavaDoc and my sample test code look like this:</p>
  
  <pre><code>LDAPConnection conn;
  BindResult bindResult;
  DIGESTMD5BindRequest mdBind;  
  try {
    conn = new LDAPConnection("1.1.1.1",389);
    mdBind = new DIGESTMD5BindRequest("dn:uid=someuser,ou=dev,dc=blah,dc=com", "test");
    bindResult = conn.bind(mdBind);
    System.out.println("MD5 bind success!");
  }
  catch (Exception e) {
    e.printStackTrace();
  }
  </code></pre>