don't include group fields with no child fields in index pattern (#69457)

x-pack/plugins/ingest_manager/server/services/epm/kibana/index_pattern/__snapshots__/install.test.ts.snap

@@ -611,7 +611,7 @@ exports[`creating index patterns from yaml fields createIndexPatternFields funct
 }
 `;
 
-exports[`creating index patterns from yaml fields flattenFields function flattens recursively and handles copying alias fields: flattenFields 1`] = `
+exports[`creating index patterns from yaml fields flattenFields function flattens recursively and handles copying alias fields flattenFields matches snapshot: flattenFields 1`] = `
 [
   {
     "name": "coredns.id",

x-pack/plugins/ingest_manager/server/services/epm/kibana/index_pattern/install.test.ts

@@ -56,9 +56,15 @@ describe('creating index patterns from yaml fields', () => {
     expect(indexPattern).toMatchSnapshot('createIndexPattern');
   });
 
-  test('flattenFields function flattens recursively and handles copying alias fields', () => {
-    const flattened = flattenFields(fields);
-    expect(flattened).toMatchSnapshot('flattenFields');
+  describe('flattenFields function flattens recursively and handles copying alias fields', () => {
+    test('a field of type group with no nested fields is skipped', () => {
+      const flattened = flattenFields([{ name: 'nginx', type: 'group' }]);
+      expect(flattened.length).toBe(0);
+    });
+    test('flattenFields matches snapshot', () => {
+      const flattened = flattenFields(fields);
+      expect(flattened).toMatchSnapshot('flattenFields');
+    });
   });
 
   describe('dedupFields', () => {

x-pack/plugins/ingest_manager/server/services/epm/kibana/index_pattern/install.ts

@@ -307,6 +307,10 @@ export const transformField = (field: Field, i: number, fields: Fields): IndexPa
 export const flattenFields = (allFields: Fields): Fields => {
   const flatten = (fields: Fields): Fields =>
     fields.reduce<Field[]>((acc, field) => {
+      // if this is a group fields with no fields, skip the field
+      if (field.type === 'group' && !field.fields?.length) {
+        return acc;
+      }
       // recurse through nested fields
       if (field.type === 'group' && field.fields?.length) {
         // skip if field.enabled is not explicitly set to false

x-pack/plugins/ingest_manager/server/services/epm/kibana/index_pattern/tests/nginx.fields.yml

@@ -116,3 +116,5 @@
       type: keyword
     - name: text
       type: text
+- name: nginx
+  type: group