Created attachment 4194 
stacktrace

Hi,

This crash was reported by a user on our bugtracker.

StacktraceTop:
 sort_by_mime_type (a=0x7f484010bc60, b=0x7f484026dd80, case_sensitive=0) at thunar-list-model.c:1487
 thunar_list_model_cmp (b=0x7f484026dd80, a=0x7f484010bc60, store=0x7f483dda6eb0) at thunar-list-model.c:1021
 thunar_list_model_cmp (store=0x7f483dda6eb0, a=0x7f484010bc60, b=0x7f484026dd80) at thunar-list-model.c:1003
 thunar_list_model_files_added (folder=<optimized out>, files=0x7fff8566cc70, store=0x7f483dda6eb0) at thunar-list-model.c:1278
 g_closure_invoke (closure=0x7f483ff8da70, return_value=0x0, n_param_values=2, param_values=0x7f4840143200, invocation_hint=<optimized out>) at /build/buildd/glib2.0-2.30.0/./gobject/gclosure.c:774

Not sure how it happened, but one of the mimetypes is NULL, so strcasecmp crashes.