Merge remote-tracking branch 'origin/master' into coerce-string

1 files changed, 6 insertions, 4 deletions

diff --git a/src/nix/prefetch.cc b/src/nix/prefetch.cc
index 782149575..fc3823406 100644
--- a/src/nix/prefetch.cc
+++ b/src/nix/prefetch.cc
@@ -199,11 +199,13 @@ static int main_nix_prefetch_url(int argc, char * * argv)
             state->forceAttrs(v, noPos, "while evaluating the source attribute to prefetch");
 
             /* Extract the URL. */
-            auto & attr = v.attrs->need(state->symbols.create("urls"));
-            state->forceList(*attr.value, noPos, "while evaluating the urls to prefetch");
-            if (attr.value->listSize() < 1)
+            auto * attr = v.attrs->get(state->symbols.create("urls"));
+            if (!attr)
+                throw Error("attribute 'urls' missing");
+            state->forceList(*attr->value, noPos, "while evaluating the urls to prefetch");
+            if (attr->value->listSize() < 1)
                 throw Error("'urls' list is empty");
-            url = state->forceString(*attr.value->listElems()[0], noPos, "while evaluating the first url from the urls list");
+            url = state->forceString(*attr->value->listElems()[0], noPos, "while evaluating the first url from the urls list");
 
             /* Extract the hash mode. */
             auto attr2 = v.attrs->get(state->symbols.create("outputHashMode"));