Fix apollographql#3393 by making merge function more defensive. (apollographql#3403)

Thanks to @HoangPaul for reporting this problem in apollographql#3393.

Author: benjamn

packages/graphql-anywhere/CHANGELOG.md

@@ -1,6 +1,10 @@
 # Change log
 
-## 4.1.9
+### 4.1.10
+- Fix [#3393](https://github.com/apollographql/apollo-client/issues/3393)
+  [PR #3403](https://github.com/apollographql/apollo-client/pull/3403)
+
+### 4.1.9
 - Various optimizations for cache read performance [#3300](https://github.com/apollographql/apollo-client/pull/3300)
 
 ### 4.1.8

packages/graphql-anywhere/src/graphql.ts

@@ -231,12 +231,14 @@ function executeSubSelectedArray(field, result, execContext) {
 const hasOwn = Object.prototype.hasOwnProperty;
 
 export function merge(dest, src) {
-  Object.keys(src).forEach(key => {
-    const srcVal = src[key];
-    if (!hasOwn.call(dest, key)) {
-      dest[key] = srcVal;
-    } else if (srcVal && typeof srcVal === 'object') {
-      merge(dest[key], srcVal);
-    }
-  });
+  if (src !== null && typeof src === 'object') {
+    Object.keys(src).forEach(key => {
+      const srcVal = src[key];
+      if (!hasOwn.call(dest, key)) {
+        dest[key] = srcVal;
+      } else {
+        merge(dest[key], srcVal);
+      }
+    });
+  }
 }