[KQL] Fix node builder with empty array (#155901)

## Summary

Fixes https://github.com/elastic/kibana/issues/95657.

Updates the logic for `nodeBuilder` when passing an empty array to
`nodeBuilder.and`/`nodeBuilder.or` to actually return a `KueryNode`
instead of `undefined`.

### Checklist

- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

packages/kbn-es-query/src/kuery/node_types/node_builder.test.ts

@@ -55,6 +55,25 @@ describe('nodeBuilder', () => {
   });
 
   describe('and method', () => {
+    test('no clauses', () => {
+      const node = nodeBuilder.and([]);
+      const query = toElasticsearchQuery(node);
+      expect(node).toMatchInlineSnapshot(`
+        Object {
+          "arguments": Array [],
+          "function": "and",
+          "type": "function",
+        }
+      `);
+      expect(query).toMatchInlineSnapshot(`
+        Object {
+          "bool": Object {
+            "filter": Array [],
+          },
+        }
+      `);
+    });
+
     test('single clause', () => {
       const nodes = [nodeBuilder.is('foo', 'bar')];
       const query = toElasticsearchQuery(nodeBuilder.and(nodes));
@@ -166,6 +185,26 @@ describe('nodeBuilder', () => {
   });
 
   describe('or method', () => {
+    test('no clauses', () => {
+      const node = nodeBuilder.or([]);
+      const query = toElasticsearchQuery(node);
+      expect(node).toMatchInlineSnapshot(`
+        Object {
+          "arguments": Array [],
+          "function": "or",
+          "type": "function",
+        }
+      `);
+      expect(query).toMatchInlineSnapshot(`
+        Object {
+          "bool": Object {
+            "minimum_should_match": 1,
+            "should": Array [],
+          },
+        }
+      `);
+    });
+
     test('single clause', () => {
       const nodes = [nodeBuilder.is('foo', 'bar')];
       const query = toElasticsearchQuery(nodeBuilder.or(nodes));

packages/kbn-es-query/src/kuery/node_types/node_builder.ts

@@ -10,23 +10,23 @@ import type { RangeFilterParams } from '../../filters';
 import { KueryNode, nodeTypes } from '../types';
 
 export const nodeBuilder = {
-  is: (fieldName: string, value: string | KueryNode) => {
+  is: (fieldName: string, value: string | KueryNode): KueryNode => {
     return nodeTypes.function.buildNodeWithArgumentNodes('is', [
       nodeTypes.literal.buildNode(fieldName),
       typeof value === 'string' ? nodeTypes.literal.buildNode(value) : value,
     ]);
   },
   or: (nodes: KueryNode[]): KueryNode => {
-    return nodes.length > 1 ? nodeTypes.function.buildNode('or', nodes) : nodes[0];
+    return nodes.length === 1 ? nodes[0] : nodeTypes.function.buildNode('or', nodes);
   },
   and: (nodes: KueryNode[]): KueryNode => {
-    return nodes.length > 1 ? nodeTypes.function.buildNode('and', nodes) : nodes[0];
+    return nodes.length === 1 ? nodes[0] : nodeTypes.function.buildNode('and', nodes);
   },
   range: (
     fieldName: string,
     operator: keyof Pick<RangeFilterParams, 'gt' | 'gte' | 'lt' | 'lte'>,
     value: number | string
-  ) => {
+  ): KueryNode => {
     return nodeTypes.function.buildNodeWithArgumentNodes('range', [
       nodeTypes.literal.buildNode(fieldName),
       operator,

src/plugins/data/server/search/session/session_service.test.ts

@@ -575,7 +575,11 @@ describe('SearchSessionService', () => {
         const [[findOptions]] = savedObjectsClient.find.mock.calls;
         expect(findOptions).toMatchInlineSnapshot(`
           Object {
-            "filter": undefined,
+            "filter": Object {
+              "arguments": Array [],
+              "function": "and",
+              "type": "function",
+            },
             "page": 0,
             "perPage": 5,
             "type": "search-session",

x-pack/plugins/alerting/server/lib/convert_rule_ids_to_kuery_node.test.ts

@@ -61,6 +61,10 @@ describe('convertRuleIdsToKueryNode', () => {
   });
 
   test('should convert empty ids array correctly', () => {
-    expect(convertRuleIdsToKueryNode([])).toEqual(undefined);
+    expect(convertRuleIdsToKueryNode([])).toEqual({
+      arguments: [],
+      function: 'or',
+      type: 'function',
+    });
   });
 });