From 85b44e7e5736a144e1f2c248b32ef004f4b26d69 Mon Sep 17 00:00:00 2001
From: Jan Kassens <jkassens@fb.com>
Date: Thu, 23 Apr 2020 09:51:57 -0700
Subject: [PATCH] fix fatal in joinArgumentDefinitions

Reviewed By: josephsavona

Differential Revision: D21190974

fbshipit-source-id: 52fd2eb8d4bc6514728c65fb778c7d9c9e2025d7
---
 .../relay-compiler/util/joinArgumentDefinitions.js   | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/packages/relay-compiler/util/joinArgumentDefinitions.js b/packages/relay-compiler/util/joinArgumentDefinitions.js
index 96a5a9d033570..58c2d41f8d9ab 100644
--- a/packages/relay-compiler/util/joinArgumentDefinitions.js
+++ b/packages/relay-compiler/util/joinArgumentDefinitions.js
@@ -85,11 +85,17 @@ function joinArgumentDefinition(
   } else if (schema.isTypeSubTypeOf(prevArgDef.type, nextArgDef.type)) {
     return prevArgDef;
   } else {
+    const prevArgType =
+      prevArgDef.type != null
+        ? schema.getTypeString(prevArgDef.type)
+        : 'unknown';
+    const nextArgType =
+      nextArgDef.type != null
+        ? schema.getTypeString(nextArgDef.type)
+        : 'unknown';
     throw createUserError(
       'Cannot combine variables with incompatible types ' +
-        `${schema.getTypeString(prevArgDef.type)} and ${schema.getTypeString(
-          nextArgDef.type,
-        )} ` +
+        `${prevArgType} and ${nextArgType} ` +
         `when applying ${directiveName}.`,
       [prevArgDef.loc, nextArgDef.loc],
     );