Index: branches/release-30/lib/MT/XMLRPCServer.pm
===================================================================
--- branches/release-30/lib/MT/XMLRPCServer.pm (revision 1174)
+++ branches/release-30/lib/MT/XMLRPCServer.pm (revision 1419)
@@ -235,10 +235,12 @@
     }
     elsif (my $cats = $item->{categories}) {
-        my $cat_class = MT->model('category');
-        # The spec says to ignore invalid category names.
-        @categories = grep { defined } $cat_class->search({
-            blog_id => $entry->blog_id,
-            label   => $cats,
-        });
+        if (@$cats) {
+	    my $cat_class = MT->model('category');
+	    # The spec says to ignore invalid category names.
+	    @categories = grep { defined } $cat_class->search({
+		blog_id => $entry->blog_id,
+		label   => $cats,
+	    });
+	}
     }