[Metrics UI] Fix No Data in Inventory alerts/Snapshot API (#72513)

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

x-pack/plugins/infra/server/lib/alerting/inventory_metric_threshold/evaluate_condition.ts

@@ -112,6 +112,8 @@ const getData = async (
   try {
     const { nodes } = await snapshot.getNodes(esClient, options);
 
+    if (!nodes.length) return { [UNGROUPED_FACTORY_KEY]: null }; // No Data state
+
     return nodes.reduce((acc, n) => {
       const nodePathItem = last(n.path) as any;
       const m = first(n.metrics);

x-pack/plugins/infra/server/lib/snapshot/response_helpers.test.ts

@@ -4,7 +4,13 @@
  * you may not use this file except in compliance with the Elastic License.
  */
 
-import { isIPv4, getIPFromBucket, InfraSnapshotNodeGroupByBucket } from './response_helpers';
+import {
+  isIPv4,
+  getIPFromBucket,
+  InfraSnapshotNodeGroupByBucket,
+  getMetricValueFromBucket,
+  InfraSnapshotMetricsBucket,
+} from './response_helpers';
 
 describe('InfraOps ResponseHelpers', () => {
   describe('isIPv4', () => {
@@ -74,4 +80,40 @@ describe('InfraOps ResponseHelpers', () => {
       expect(getIPFromBucket('host', bucket)).toBe(null);
     });
   });
+
+  describe('getMetricValueFromBucket', () => {
+    it('should return the value of a bucket with data', () => {
+      expect(getMetricValueFromBucket('custom', testBucket, 1)).toBe(0.5);
+    });
+    it('should return the normalized value of a bucket with data', () => {
+      expect(getMetricValueFromBucket('cpu', testNormalizedBucket, 1)).toBe(50);
+    });
+    it('should return null for a bucket with no data', () => {
+      expect(getMetricValueFromBucket('custom', testEmptyBucket, 1)).toBe(null);
+    });
+  });
 });
+
+// Hack to get around TypeScript
+const buckets = [
+  {
+    key: 'a',
+    doc_count: 1,
+    custom_1: {
+      value: 0.5,
+    },
+  },
+  {
+    key: 'b',
+    doc_count: 1,
+    cpu: {
+      value: 0.5,
+      normalized_value: 50,
+    },
+  },
+  {
+    key: 'c',
+    doc_count: 0,
+  },
+] as InfraSnapshotMetricsBucket[];
+const [testBucket, testNormalizedBucket, testEmptyBucket] = buckets;

x-pack/plugins/infra/server/lib/snapshot/response_helpers.ts

@@ -158,14 +158,15 @@ const findLastFullBucket = (
   }, last(buckets));
 };
 
-const getMetricValueFromBucket = (
+export const getMetricValueFromBucket = (
   type: SnapshotMetricType,
   bucket: InfraSnapshotMetricsBucket,
   index: number
 ) => {
   const key = type === 'custom' ? `custom_${index}` : type;
   const metric = bucket[key];
-  return (metric && (metric.normalized_value || metric.value)) || 0;
+  const value = metric && (metric.normalized_value || metric.value);
+  return isFinite(value) ? value : null;
 };
 
 function calculateMax(