Adding "fork:true" in repositories search query, results in [422 Unprocessable Entity] error

I have this method and it works:

```
@Override
public List getReposNameByLogin(String login) throws GitHubServiceException
{
List repos = new LinkedList<>();
try
{
for (Repo repo : github.search().repos("user:" + login, "stars", Search.Order.DESC))
{
repos.add(repo.coordinates().repo());
}
}
catch (IOException e)
{
throw new GitHubServiceException(e);
}
return repos;
}
```

If I change the for line for this one, it fails:

```
for (Repo repo : github.search().repos("user:" + login+"+fork:true", "stars", Search.Order.DESC))
```

login variable value is "nilopc".

getting this error:

```
2015-07-13 03:11:36.444 INFO 1945 --- [nio-8080-exec-1] com.jcabi.http.request.BaseRequest : #fetch(GET api.github.com /search/repositories): [422 Unprocessable Entity] in 853ms
2015-07-13 03:11:36.454 ERROR 1945 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Handler processing failed; nested exception is java.lang.AssertionError: HTTP response status is not equal to 200:
com.jcabi.github.RtSearchPagination$Hidden@7b26d4a8
Expected: HTTP response with status 200
but: was ] with root cause

java.lang.AssertionError: HTTP response status is not equal to 200:
com.jcabi.github.RtSearchPagination$Hidden@7b26d4a8
Expected: HTTP response with status 200
but: was
at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20)
at com.jcabi.http.response.RestResponse.assertStatus(RestResponse.java:117)
at com.jcabi.github.RtValuePagination$Items.fetch(RtValuePagination.java:199)
at com.jcabi.github.RtValuePagination$Items.hasNext(RtValuePagination.java:185)
....
```