Loki: Remove empty annotations tags (#32359) (#32490)

* Loki - filter labels with empty values

Signed-off-by: Conor Evans <coevans@tcd.ie>

* Apply prettier change

Signed-off-by: Conor Evans <coevans@tcd.ie>

* Apply Piotr's suggestion - swap map/filter statements

Signed-off-by: Conor Evans <coevans@tcd.ie>
(cherry picked from commit 3af573ea96)

Co-authored-by: Conor Evans <43791257+conorevans@users.noreply.github.com>

public/app/plugins/datasource/loki/datasource.test.ts

@@ -469,7 +469,9 @@ describe('LokiDatasource', () => {
               },
               {
                 stream: {
+                  label: '', // empty value gets filtered
                   label2: 'value2',
+                  label3: ' ', // whitespace value gets trimmed then filtered
                 },
                 values: [['1549024057498000000', 'hello 2']],
               },

public/app/plugins/datasource/loki/datasource.ts

@@ -511,7 +511,13 @@ export class LokiDatasource extends DataSourceApi<LokiQuery, LokiOptions> {
       const tags: string[] = [];
       for (const field of frame.fields) {
         if (field.labels) {
-          tags.push.apply(tags, [...new Set(Object.values(field.labels).map((label: string) => label.trim()))]);
+          tags.push.apply(tags, [
+            ...new Set(
+              Object.values(field.labels)
+                .map((label: string) => label.trim())
+                .filter((label: string) => label !== '')
+            ),
+          ]);
         }
       }
       const view = new DataFrameView<{ ts: string; line: string }>(frame);