From cd9004ce5badc66b6e323cffcf091bc08da73706 Mon Sep 17 00:00:00 2001
From: "Michael \"Z\" Goddard" <mzgoddard@gmail.com>
Date: Fri, 3 Nov 2017 11:40:20 -0400
Subject: [PATCH] Write src/engine/execute so it can be optimized

Testing with implicitly casted `value` and `value.then` is deoptimizing
isPromise, which deoptimizes execute. In this case deoptimizing means
that the JavaScript VM cannot compile the functions into a form that
can be run faster.
---
 src/engine/execute.js | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/engine/execute.js b/src/engine/execute.js
index a4bf76b2a..24864592f 100644
--- a/src/engine/execute.js
+++ b/src/engine/execute.js
@@ -8,7 +8,11 @@ const {Map} = require('immutable');
  * @return {boolean} True if the value appears to be a Promise.
  */
 const isPromise = function (value) {
-    return value && value.then && typeof value.then === 'function';
+    return (
+        value !== null &&
+        typeof value === 'object' &&
+        typeof value.then === 'function'
+    );
 };
 
 /**