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.
declaredDependencies,
  declaredDependenciesNode,
  componentScope,
  scope,
}) {
  const constructions = declaredDependencies
    .map(({key}) => {
      const ref = componentScope.variables.find(v => v.name === key);
      if (ref == null) {
        return null;
      }
      const node = ref.defs[0];
      if (node == null) {
        return null;
      }
      
      
      
      
      
      if (
        node.type === 'Variable' &&
        node.node.type === 'VariableDeclarator' &&
        node.node.id.type === 'Identifier' && 
        node.node.init != null
      ) {
        const constantExpressionType = getConstructionExpressionType(
          node.node.init,
        );