Use same pattern in custom snapshot serializers

Author: eps1lon

packages/react-devtools-shared/src/__tests__/treeContextStateSerializer.js

@@ -2,11 +2,13 @@ import {printStore} from 'react-devtools-shared/src/devtools/utils';
 
 // test() is part of Jest's serializer API
 export function test(maybeState) {
+  if (maybeState === null || typeof maybeState !== 'object') {
+    return false;
+  }
+
   const hasOwnProperty = Object.prototype.hasOwnProperty.bind(maybeState);
   // Duck typing at its finest.
   return (
-    maybeState !== null &&
-    typeof maybeState === 'object' &&
     hasOwnProperty('inspectedElementID') &&
     hasOwnProperty('ownerFlatTree') &&
     hasOwnProperty('ownerSubtreeLeafElementID')