Bugfix for exception at discover context view using date_nanos (#41353)

* Fix extracting nanos of timestamps with only dates

* Add jest test catching it

src/legacy/core_plugins/kibana/public/context/api/utils/__tests__/date_conversion.test.ts

@@ -0,0 +1,31 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+import { extractNanos } from '../date_conversion';
+
+describe('function extractNanos', function() {
+  test('extract nanos of 2014-01-01', function() {
+    expect(extractNanos('2014-01-01')).toBe('000000000');
+  });
+  test('extract nanos of 2014-01-01T12:12:12.234Z', function() {
+    expect(extractNanos('2014-01-01T12:12:12.234Z')).toBe('234000000');
+  });
+  test('extract nanos of 2014-01-01T12:12:12.234123321Z', function() {
+    expect(extractNanos('2014-01-01T12:12:12.234123321Z')).toBe('234123321');
+  });
+});

src/legacy/core_plugins/kibana/public/context/api/utils/date_conversion.ts

@@ -23,9 +23,11 @@ import moment from 'moment';
  * returns the nanos as string like this:
  * 9ns -> 000000009
  * 10000ns -> 0000010000
- */
+ * returns 000000000 for invalid timestamps or timestamps with just date
+ **/
 export function extractNanos(timeFieldValue: string = ''): string {
-  const fractionSeconds = timeFieldValue.split('.')[1].replace('Z', '');
+  const fieldParts = timeFieldValue.split('.');
+  const fractionSeconds = fieldParts.length === 2 ? fieldParts[1].replace('Z', '') : '';
   return fractionSeconds.length !== 9 ? fractionSeconds.padEnd(9, '0') : fractionSeconds;
 }