states for Tcl_OpenCommandChannel():

<pre>
  If an error occurs while opening the channel, [...] In addition,
  Tcl_OpenCommandChannel leaves an error message in the interpreter's
  result if interp is not NULL.
</pre>

The code in generic/TclPipe.c however states that interp cannot be NULL:

<pre>
  Tcl_Channel
  Tcl_OpenCommandChannel(
      Tcl_Interp *interp, /* Interpreter for error reporting. Can NOT be NULL. */
</pre>

And indeed, calling Tcl_OpenCommandChannel(NULL, ...) dumps core in case of an error when opening the pipeline (e.g. command not found).

=> Documentation should be adjusted: "interp cannot be NULL".