#### Describe the bug
The irrelevant error returned when requesting illegal URL, like: "tel:484-695-3408"
```
TypeError: Cannot read property 'replace' of null
    at dispatchHttpRequest (node_modules/axios/lib/adapters/http.js:109:74)
    at new Promise (<anonymous>)
    at httpAdapter (node_modules/axios/lib/adapters/http.js:46:10)
    at dispatchRequest (node_modules/axios/lib/core/dispatchRequest.js:52:10)
```

#### To Reproduce
```js
axios.get('tel:484-695-3408').catch(err => console.error(err));
```

#### Expected behavior
Return descriptive error, like "Unsupported protocol tel:"

#### Environment
 - Axios Version: 0.21.1
 - Adapter: HTTP
 - Browser: none
 - Browser Version: none
 - Node.js Version: 12.19.0
 - OS: MacOS 10.14
 - Additional Library Versions: none

#### Additional context/Screenshots
none
test/specs/requests.spec.js
}
    axios('/foo', {
      responseType: 'arraybuffer'
    }).then(function (data) {
      response = data;
    });
    getAjaxRequest().then(function (request) {
      request.respondWith({
        status: 200,
        response: str2ab('Hello world')
      });
      setTimeout(function () {
        expect(response.data.byteLength).toBe(22);
        done();
      }, 100);
    });
  });
  it('should support URLSearchParams', function (done) {
    var params = new URLSearchParams();
    params.append('param1', 'value1');
    params.append('param2', 'value2');
    axios.post('/foo', params);
    getAjaxRequest().then(function (request) {
      expect(request.requestHeaders['Content-Type']).toBe('application/x-www-form-urlencoded;charset=utf-8');
      expect(request.params).toBe('param1=value1&param2=value2');
      done();
    });
  });
});