From b4d6e70a1168d81781a455d19b748cfd73d22246 Mon Sep 17 00:00:00 2001
From: Kevin Schaaf <kschaaf@google.com>
Date: Tue, 28 Aug 2018 17:53:27 -0400
Subject: [PATCH] Upstream warning text.

---
 lib/legacy/legacy-data-mixin.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/legacy/legacy-data-mixin.js b/lib/legacy/legacy-data-mixin.js
index 5aee1e0209..2d18397d6a 100644
--- a/lib/legacy/legacy-data-mixin.js
+++ b/lib/legacy/legacy-data-mixin.js
@@ -40,7 +40,7 @@ function wrapEffect(effect, fnName) {
         fn.apply(this, arguments);
       } catch (e) {
         if (e instanceof UndefinedArgumentError) {
-          console.warn(`Argument '${e.arg}'${fnName ?` for method '${fnName}'` : ''} was undefined. Ensure it has an undefined check.`);
+          console.warn(`Argument '${e.arg}'${fnName ?` for method '${fnName}'` : ''} was undefined. Ensure it has a default value, or else ensure the method handles the argument being undefined.`);
         } else {
           throw e;
         }
@@ -98,7 +98,7 @@ export const LegacyDataMixin = dedupingMixin(superClass => {
             // Break out of effect's control flow; will be caught in
             // wrapped property effect function below
             const name = args[i].name;
-            throw new UndefinedArgumentError(`Argument '${name}' is undefined. Ensure it has an undefined check.`, name);
+            throw new UndefinedArgumentError(`Argument '${name}' is undefined.`, name);
           }
         }
       }