[Uptime] Fix broken overview page when no summary data present (#81952) (#82021)

Fixes #81950

by not assuming the summary is present in a bucket with partial check
info

Author: andrewvc

x-pack/plugins/uptime/server/lib/requests/search/refine_potential_matches.ts

@@ -38,6 +38,12 @@ export const fullyMatchingIds = (queryResult: any, statusFilter?: string): Monit
 
     for (const locBucket of monBucket.location.buckets) {
       const latest = locBucket.summaries.latest.hits.hits[0];
+      // It is possible for no latest summary to exist in this bucket if only partial
+      // non-summary docs exist
+      if (!latest) {
+        continue;
+      }
+
       const latestStillMatching = locBucket.latest_matching.top.hits.hits[0];
       // If the most recent document still matches the most recent document matching the current filters
       // we can include this in the result

x-pack/test/api_integration/apis/uptime/rest/monitor_states_generated.ts

@@ -24,6 +24,30 @@ export default function ({ getService }: FtrProviderContext) {
     before('load heartbeat data', () => getService('esArchiver').load('uptime/blank'));
     after('unload heartbeat index', () => getService('esArchiver').unload('uptime/blank'));
 
+    // In this case we don't actually have any monitors to display
+    // but the query should still return successfully. This has
+    // caused bugs in the past because a bucket of monitor data
+    // was available and the query code assumed at least one
+    // event would be a summary for each monitor.
+    // See https://github.com/elastic/kibana/issues/81950
+    describe('checks with no summaries', async () => {
+      const testMonitorId = 'scope-test-id';
+      before(async () => {
+        const es = getService('legacyEs');
+        dateRangeStart = new Date().toISOString();
+        await makeChecksWithStatus(es, testMonitorId, 1, numIps, 1, {}, 'up', (d) => {
+          delete d.summary;
+          return d;
+        });
+      });
+
+      it('should return no monitors and have no errors', async () => {
+        const url = getBaseUrl(dateRangeStart, new Date().toISOString());
+        const apiResponse = await supertest.get(url);
+        expect(apiResponse.status).to.equal(200);
+      });
+    });
+
     describe('query document scoping with mismatched check statuses', async () => {
       let checks: any[] = [];
       let nonSummaryIp: string | null = null;