Add test for `GET non-existent-key` case. (issue #267)

test.js

@@ -817,12 +817,19 @@ tests.DBSIZE = function () {
     client.DBSIZE([], last(name, require_number_pos("DBSIZE")));
 };
 
-tests.GET = function () {
-    var name = "GET";
+tests.GET_1 = function () {
+    var name = "GET_1";
     client.set(["get key", "get val"], require_string("OK", name));
     client.GET(["get key"], last(name, require_string("get val", name)));
 };
 
+tests.GET_2 = function() {
+    var name = "GET_2";
+
+    // tests handling of non-existent keys
+    client.GET('this_key_shouldnt_exist', last(name, require_null(name)));
+};
+
 tests.SET = function () {
     var name = "SET";
     client.SET(["set key", "set val"], require_string("OK", name));