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.
...testsFlow.invalid,
    ...testsTypescript.valid,
    ...testsTypescript.invalid,
    ...testsTypescriptEslintParserV4.valid,
    ...testsTypescriptEslintParserV4.invalid,
  ].forEach(t => {
    if (t.skip) {
      delete t.skip;
      skipped.push(t);
    }
    if (t.only) {
      delete t.only;
      only.push(t);
    }
  });
  const predicate = t => {
    if (only.length > 0) {
      return only.indexOf(t) !== -1;
    }
    if (skipped.length > 0) {
      return skipped.indexOf(t) === -1;
    }
    return true;
  };
  tests.valid = tests.valid.filter(predicate);
  tests.invalid = tests.invalid.filter(predicate);
  testsFlow.valid = testsFlow.valid.filter(predicate);
  testsFlow.invalid = testsFlow.invalid.filter(predicate);
  testsTypescript.valid = testsTypescript.valid.filter(predicate);
  testsTypescript.invalid = testsTypescript.invalid.filter(predicate);