@@ -258,11 +258,11 @@
 // http://inside.mines.edu/~gmurray/ArbitraryAxisRotation/ArbitraryAxisRotation.html
 // creates a rotation matrix about the given vector.
 //
 function vector_rotation(vector, s){
 	if(!vector) throw "vector argument to vector_rotation missing";
-	if(!s) throw "angle argument to vector_rotation missing";
+	if(s === null || s === undefined) throw "angle argument to vector_rotation missing";
 	
     var len = Math.sqrt(vector[0]*vector[0]
                         + vector[1]*vector[1]
                         + vector[2]*vector[2]);