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.
fnScope = childScope;
            break;
          }
        }
        if (fnScope == null) {
          return false;
        }
        
        
        for (i = 0; i < fnScope.through.length; i++) {
          const ref = fnScope.through[i];
          if (ref.resolved == null) {
            continue;
          }
          if (
            pureScopes.has(ref.resolved.scope) &&
            
            
            !memoizedIsStablecKnownHookValue(ref.resolved)
          ) {
            return false;
          }
        }
        
        
        return true;
      }
      
      const memoizedIsStablecKnownHookValue = memoizeWithWeakMap(
        isStableKnownHookValue,