Null handling and plpython

I'm reviewing the plpython data type handling patch from the commit fest.  I 
have not dealt much with the plpython code before, and I'm a bit puzzled by 
its elaborately silly handling of null values.  A representative example (for 
the current code):
        if (tupdesc->attrs[atti]->attisdropped)        {            modvalues[i] = (Datum) 0;            modnulls[i] =
'n';       }        else if (plval != Py_None)        {            plstr = PyObject_Str(plval);            if (!plstr)
             PLy_elog(ERROR, "could not compute string representation of Python 
 
object, while modifying trigger row");            src = PyString_AsString(plstr);
            modvalues[i] =                InputFunctionCall(&proc->result.out.r.atts[atti].typfunc,
            src,                                proc->result.out.r.atts[atti].typioparam,
  tupdesc->attrs[atti]->atttypmod);            modnulls[i] = ' ';
 
            Py_DECREF(plstr);            plstr = NULL;        }        else /* FUN STARTS HERE */        {
modvalues[i]=                InputFunctionCall(&proc->result.out.r.atts[atti].typfunc,
NULL,                               proc->result.out.r.atts[atti].typioparam,
tupdesc->attrs[atti]->atttypmod);           modnulls[i] = 'n';        }
 
        Py_DECREF(plval);        plval = NULL;    }
    rtup = SPI_modifytuple(tdata->tg_relation, otup, natts,                           modattrs, modvalues, modnulls);

First of all, SPI_modifytuple (which wraps around heap_modify_tuple) appears 
to ignore the values when a slot is marked to be null.

And then, what is the supposed semantics of calling a nonstrict input function 
with NULL as the cstring value?  InputFunctionCall() requires that the return 
value is null if and only if the input cstring was NULL, "but we'll call the 
input function anyway".  Couldn't the call to InputFunctionCall() be scrapped 
altogether in the above case?