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Uncaught TypeError: Cannot read property 'toUpperCase' of undefined in React

Ok, I gotta admit this is a really annoying issue because its root cause is pretty trivial. You get this issue in React when

You are accidentally trying to render a component and that component itself is null or undefined. e.g you are trying to render <MyComponent /> when the value of MyComponent is itself null or undefined.

Ive encountered this issue several times, the most recent being when upgrading to react-router 1.0 release candidate which eliminated the the <RouteHandler /> component. As a result, at places in my tree where I was doing a require for RouteHandler, things worked because it simply returned undefiend, but the moment I tried to render it using <RouteHandler /> React gave me this pretty little error. Hope this helps you save some productive time!

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Also Read:

1. Pass props to the handler component in react-router
2. Using React with Backbone Models
3. Automating Store and Action registration for multiple components using Fluxxor
4. webpack with babel6 and react
5. Passing the store down implicitly via context in a react redux app

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