nlist return values

[utzoo!decvax!cca!hplabs!menlo70!sytek!olmstead at sri-unix]

I haven't seen this one on the net before, but then I don't look all that
frequently, so apologies if this is old stuff:

Our version (4.1bsd) of nlist(3) returns, under various conditions, the values
-1, 0, and NULL.  Now I know the documentation doesn't claim to return any
value at all, which is mostly why I was reading the source in the first place.
I can't believe an interface that tells me I have to see if every entry in a
list has been set to zero to know whether the call failed or not.  Even given
this, it's pretty weird to return 0 in some places and NULL (that's right, NULL
is the same one from stdio, where it's defined to be 0) in other places.  Does
anyone ever look at nlist's return value?