crash in serf credential callback

Hi,

There's a crash happening in libsvn_ra_serf\util.c in the function
svn_ra_serf__credentials_callback. There's a full crash dump available
from here:
https://www.crash-server.com/Problem.aspx?ClientID=tsvn&ProblemID=58311

 From what I can figure out from that crash dump is that the 'session'
baton is not set (it's NULL), which leads to a segfault in the line:

       *username = apr_pstrdup(pool, session->proxy_username);

The http return code is 407.

But I can't figure out if this is a problem in serf or the svn library.
Maybe one of you guys can have a look at this?

Stefan

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