Uncaught TypeError: fn is not a function

[scottdhicks]

@fvilers

attempted to contribute but got a 403 (first time ever trying to contribute to open source so i'm a newb). if someone has bandwidth, can

if (prop === 'rendererInterfaces') {
    // prevents TypeError: fn is not a function onAgentShutdown
    window.__REACT_DEVTOOLS_GLOBAL_HOOK__[prop] = new Map();
    continue;
}

be added to index.js? https://github.com/facebook/react/blob/e26cb8f86db0936e14682c39e2d26373fa6f433d/packages/react-devtools-shared/src/backend/index.js#L110 is the problematic line in react-devtools