Be able to list issues with no labels using API

doc/api/issues.md

@@ -23,6 +23,7 @@ GET /issues?state=closed
 GET /issues?labels=foo
 GET /issues?labels=foo,bar
 GET /issues?labels=foo,bar&state=opened
+GET /projects/:id/issues?labels_name=No+Label
 GET /issues?milestone=1.0.0
 GET /issues?milestone=1.0.0&state=opened
 GET /issues?iids[]=42&iids[]=43
@@ -32,6 +33,7 @@ GET /issues?iids[]=42&iids[]=43
 | --------- | ---- | -------- | ----------- |
 | `state`   | string  | no    | Return all issues or just those that are `opened` or `closed`|
 | `labels`  | string  | no    | Comma-separated list of label names, issues must have all labels to be returned |
+| `labels_name`  | string  | no    | Return all issues with the mentioned label. `No+Label` lists all issues with no labels |
 | `milestone` | string| no    | The milestone title |
 | `iids`    | Array[integer] | no | Return only the issues having the given `iid` |
 | `order_by`| string  | no    | Return requests ordered by `created_at` or `updated_at` fields. Default is `created_at` |
@@ -102,6 +104,7 @@ GET /groups/:id/issues?state=closed
 GET /groups/:id/issues?labels=foo
 GET /groups/:id/issues?labels=foo,bar
 GET /groups/:id/issues?labels=foo,bar&state=opened
+GET /projects/:id/issues?labels_name=No+Label
 GET /groups/:id/issues?milestone=1.0.0
 GET /groups/:id/issues?milestone=1.0.0&state=opened
 GET /groups/:id/issues?iids[]=42&iids[]=43
@@ -112,6 +115,7 @@ GET /groups/:id/issues?iids[]=42&iids[]=43
 | `id`      | integer | yes   | The ID of a group |
 | `state`   | string  | no    | Return all issues or just those that are `opened` or `closed`|
 | `labels`  | string  | no    | Comma-separated list of label names, issues must have all labels to be returned |
+| `labels_name`  | string  | no    | Return all issues with the mentioned label. `No+Label` lists all issues with no labels |
 | `iids`    | Array[integer] | no | Return only the issues having the given `iid` |
 | `milestone` | string| no    | The milestone title |
 | `order_by`| string  | no    | Return requests ordered by `created_at` or `updated_at` fields. Default is `created_at` |
@@ -183,6 +187,7 @@ GET /projects/:id/issues?state=closed
 GET /projects/:id/issues?labels=foo
 GET /projects/:id/issues?labels=foo,bar
 GET /projects/:id/issues?labels=foo,bar&state=opened
+GET /projects/:id/issues?labels_name=No+Label
 GET /projects/:id/issues?milestone=1.0.0
 GET /projects/:id/issues?milestone=1.0.0&state=opened
 GET /projects/:id/issues?iids[]=42&iids[]=43
@@ -194,6 +199,7 @@ GET /projects/:id/issues?iids[]=42&iids[]=43
 | `iids`    | Array[integer] | no | Return only the milestone having the given `iid` |
 | `state`   | string  | no    | Return all issues or just those that are `opened` or `closed`|
 | `labels`  | string  | no    | Comma-separated list of label names, issues must have all labels to be returned |
+| `labels_name`  | string  | no    | Return all issues with the mentioned label. `No+Label` lists all issues with no labels |
 | `milestone` | string| no    | The milestone title |
 | `order_by`| string  | no    | Return requests ordered by `created_at` or `updated_at` fields. Default is `created_at` |
 | `sort`    | string  | no    | Return requests sorted in `asc` or `desc` order. Default is `desc`  |