make the second argument to throw properly optional

lib/context.js

@@ -62,27 +62,29 @@ var proto = module.exports = {
    *    this.throw(400, new Error('invalid'));
    *
    * @param {String|Number|Error} err, msg or status
-   * @param {String|Number|Error} err, msg or status
+   * @param {String|Number|Error} [err, msg or status]
    * @param {Object} [props]
    * @api public
    */
 
   throw: function(msg, status, props){
+    if ('object' == typeof status && !(status instanceof Error)) {
+      props = status;
+      status = null;
+    }
+
     if ('number' == typeof msg) {
       var tmp = msg;
       msg = status || http.STATUS_CODES[tmp];
       status = tmp;
     }
 
+    props = props || {};
+
     var err = msg instanceof Error ? msg : new Error(msg);
-
+    for (var key in props) err[key] = props[key];
-    if (props) {
-      for (var key in props) err[key] = props[key];
-    }
-
     err.status = status || err.status || 500;
     err.expose = 'number' == typeof err.status && http.STATUS_CODES[err.status] && err.status < 500;
-
     throw err;
   },
 

test/context/throw.js

@@ -159,3 +159,35 @@ describe('ctx.throw(status, msg, props)', function(){
     })
   })
 })
+
+describe('ctx.throw(msg, props)', function(){
+  it('should mixin props', function(done){
+    var ctx = context();
+
+    try {
+      ctx.throw('msg', { prop: true });
+    } catch (err) {
+      assert('msg' == err.message);
+      assert(500 == err.status);
+      assert(false === err.expose);
+      assert(true === err.prop);
+      done();
+    }
+  })
+})
+
+describe('ctx.throw(status, props)', function(){
+  it('should mixin props', function(done){
+    var ctx = context();
+
+    try {
+      ctx.throw(400, { prop: true });
+    } catch (err) {
+      assert('Bad Request' == err.message);
+      assert(400 == err.status);
+      assert(true === err.expose);
+      assert(true === err.prop);
+      done();
+    }
+  })
+})