Fix sketchy null checks induced by new formatting in Prettier 2.0

Summary:
Update code to prepare for Prettier 2.0, which will
reformat `a || (b || c)` to `a || b || c`.

Changelog: [Internal] prepare for Prettier 2.0

Reviewed By: kassens

Differential Revision: D20639483

fbshipit-source-id: c2932b1495884684172ba9291d56c546f51711b8

RNTester/js/utils/RNTesterStatePersister.js

@@ -42,11 +42,9 @@ function createContainer<Props: Object, State>(
     Props,
     $FlowFixMeState,
   > {
-    /* $FlowFixMe(>=0.53.0 site=react_native_fb,react_native_oss) This comment
-     * suppresses an error when upgrading Flow's support for React. To see the
-     * error delete this comment and run Flow. */
-    static displayName = `RNTesterStatePersister(${Component.displayName ||
-      Component.name})`;
+    static displayName = `RNTesterStatePersister(${String(
+      Component.displayName ?? Component.name,
+    )})`;
     state = {value: spec.getInitialState(this.props)};
     _cacheKey = `RNTester:${spec.version || 'v1'}:${spec.cacheKeySuffix(
       this.props,