From 084566b579f5f8141e0d9c55067216ded2f40cbf Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonygarnockjones@gmail.com>
Date: Sat, 3 Nov 2018 22:18:58 +0000
Subject: [PATCH] Complain when constructing a Structure with an undefined
 field, not when manipulating such a structure later

---
 packages/core/src/struct.js | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/packages/core/src/struct.js b/packages/core/src/struct.js
index 37f5447..de3b51f 100644
--- a/packages/core/src/struct.js
+++ b/packages/core/src/struct.js
@@ -73,6 +73,9 @@ function Structure(meta, fields) {
   this.fields = fields.slice(0);
   for (var i = 0; i < fields.length; i++) {
     this[i] = fields[i] = Immutable.fromJS(fields[i]);
+    if (this[i] === void 0) {
+      throw new Error("Structure: cannot contain undefined value at field " + i);
+    }
   }
 }