eslint-plugin-react-hooks version: 4.2.0

## Steps To Reproduce

I know it shouldn't exist in production code, but it's annoying while editing some files.

```js
import React, { useEffect } from "react";

const App = () => {
  useEffect(); // <-
  return null;
};

export default App;
```

Link to code example: https://codesandbox.io/s/polished-sun-3wr27?file=/src/App.js

## The current behavior

ESLint crashed.

```
TypeError: Cannot read property 'type' of undefined
```

## The expected behavior

ESLint doesn't crash but reports an error instead.
function isStableKnownHookValue(resolved) {
        if (!Array.isArray(resolved.defs)) {
          return false;
        }
        const def = resolved.defs[0];
        if (def == null) {
          return false;
        }
        
        if (def.node.type !== 'VariableDeclarator') {
          return false;
        }
        let init = def.node.init;
        if (init == null) {
          return false;
        }
        while (init.type === 'TSAsExpression') {
          init = init.expression;
        }
        
        
        let declaration = def.node.parent;
        if (declaration == null) {