[Security solutions] Adds linter rule to forbid usage of no-non-null-assertion (TypeScript ! bang operator) (elastic#114375)

## Summary

Fixes: elastic#114535

**What this linter rule does:**
* Sets the [@typescript-eslint/no-non-null-assertion](https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-non-null-assertion.md) linter rule to become an error if seen.

If you try to use the `!` operator you get an error and nice helper message that tries to encourage better practices such as this one:

<img width="1635" alt="Screen Shot 2021-10-07 at 11 26 14 AM" src="https://user-images.githubusercontent.com/1151048/136474207-f38d3461-0af9-4cdc-885b-632cb49d8a24.png">

**Why are we deciding to set this linter rule?**
* Recommended from Kibana [styleguide](https://github.com/elastic/kibana/blob/master/STYLEGUIDE.mdx#avoid-non-null-assertions) for ~2 years now and still recommended.
* A lot of TypeScript has evolved and has operators such as `?` which can replace the `!` in most cases. Other cases can use a throw explicitly or other ways to manage this.
* Some types can change instead of using this operator and we should just change the types.
* TypeScript flows have improved and when we upgrade the linter will cause errors where we can remove the `!` operator which is 👍 better than leaving them when they're not needed anymore.
* Newer programmers and team members sometimes mistake it for the `?` when it is not the same thing.
* We have had past bugs and bugs recently because of these.
* It's easier to use the linter to find bugs than to rely on manual tests. 

**How did Frank fix all the 403 areas in which the linter goes off?**
* Anywhere I could remove the `!` operator without side effects or type script errors I just removed the `!` operator.
* Anywhere in test code where I could replace the code with a `?` or a `throw` I went through that route.
* Within the code areas (non test code) where I saw what looks like a simple bug that I could fix using a `?? []` or `?` operator or `String(value)` or fixing a simple type I would choose that route first. These areas I marked in the code review with the words `NOTE:` for anyone to look at.
* Within all other areas of the code and tests where anything looked more involved I just disabled the linter for that particular line. When in doubt I chose this route.

### Checklist

- [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

Author: FrankHassanabad

.eslintrc.js

@@ -899,7 +899,12 @@ module.exports = {
     },
 
     /**
-     * Security Solution overrides
+     * Security Solution overrides. These rules below are maintained and owned by
+     * the people within the security-solution-platform team. Please see ping them
+     * or check with them if you are encountering issues, have suggestions, or would
+     * like to add, change, or remove any particular rule. Linters, Typescript, and rules
+     * evolve and change over time just like coding styles, so please do not hesitate to
+     * reach out.
      */
     {
       // front end and common typescript and javascript files only
@@ -922,6 +927,22 @@ module.exports = {
         ],
       },
     },
+    {
+      // typescript only for front and back end, but excludes the test files.
+      // We use this section to add rules in which we do not want to apply to test files.
+      // This should be a very small set as most linter rules are useful for tests as well.
+      files: [
+        'x-pack/plugins/security_solution/**/*.{ts,tsx}',
+        'x-pack/plugins/timelines/**/*.{ts,tsx}',
+      ],
+      excludedFiles: [
+        'x-pack/plugins/security_solution/**/*.{test,mock,test_helper}.{ts,tsx}',
+        'x-pack/plugins/timelines/**/*.{test,mock,test_helper}.{ts,tsx}',
+      ],
+      rules: {
+        '@typescript-eslint/no-non-null-assertion': 'error',
+      },
+    },
     {
       // typescript only for front and back end
       files: [
@@ -1040,7 +1061,12 @@ module.exports = {
     },
 
     /**
-     * Lists overrides
+     * Lists overrides. These rules below are maintained and owned by
+     * the people within the security-solution-platform team. Please see ping them
+     * or check with them if you are encountering issues, have suggestions, or would
+     * like to add, change, or remove any particular rule. Linters, Typescript, and rules
+     * evolve and change over time just like coding styles, so please do not hesitate to
+     * reach out.
      */
     {
       // front end and common typescript and javascript files only
@@ -1215,8 +1241,14 @@ module.exports = {
         ],
       },
     },
+
     /**
-     * Metrics entities overrides
+     * Metrics entities overrides. These rules below are maintained and owned by
+     * the people within the security-solution-platform team. Please see ping them
+     * or check with them if you are encountering issues, have suggestions, or would
+     * like to add, change, or remove any particular rule. Linters, Typescript, and rules
+     * evolve and change over time just like coding styles, so please do not hesitate to
+     * reach out.
      */
     {
       // front end and common typescript and javascript files only

x-pack/plugins/security_solution/common/detection_engine/utils.ts

@@ -51,7 +51,8 @@ export const normalizeThresholdField = (
     ? thresholdField
     : isEmpty(thresholdField)
     ? []
-    : [thresholdField!];
+    : // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      [thresholdField!];
 };
 
 export const normalizeThresholdObject = (threshold: Threshold): ThresholdNormalized => {

x-pack/plugins/security_solution/common/endpoint/data_loaders/index_endpoint_hosts.ts

@@ -161,7 +161,7 @@ export async function indexEndpointHostDocs({
         const indexedAgentResponse = await indexFleetAgentForHost(
           client,
           kbnClient,
-          hostMetadata!,
+          hostMetadata,
           realPolicies[appliedPolicyId].policy_id,
           kibanaVersion
         );

x-pack/plugins/security_solution/common/endpoint/data_loaders/index_fleet_agent.ts

@@ -73,7 +73,7 @@ export const indexFleetAgentForHost = async (
     .index<FleetServerAgent>({
       index: agentDoc._index,
       id: agentDoc._id,
-      body: agentDoc._source!,
+      body: agentDoc._source,
       op_type: 'create',
     })
     .catch(wrapErrorAndRejectPromise);

x-pack/plugins/security_solution/cypress/integration/cases/connectors.spec.ts

@@ -89,11 +89,11 @@ describe('Cases connectors', () => {
     addServiceNowConnector(snConnector);
 
     cy.wait('@createConnector').then(({ response }) => {
-      cy.wrap(response!.statusCode).should('eql', 200);
+      cy.wrap(response?.statusCode).should('eql', 200);
       cy.get(TOASTER).should('have.text', "Created 'New connector'");
       cy.get(TOASTER).should('not.exist');
 
-      selectLastConnectorCreated(response!.body.id);
+      selectLastConnectorCreated(response?.body.id);
 
       cy.wait('@saveConnector', { timeout: 10000 }).its('response.statusCode').should('eql', 200);
       cy.get(SERVICE_NOW_MAPPING).first().should('have.text', 'short_description');

x-pack/plugins/security_solution/cypress/integration/detection_rules/custom_query_rule.spec.ts

@@ -351,10 +351,10 @@ describe('Custom detection rules deletion and edition', () => {
       goToRuleDetails();
 
       cy.wait('@fetchRuleDetails').then(({ response }) => {
-        cy.wrap(response!.statusCode).should('eql', 200);
+        cy.wrap(response?.statusCode).should('eql', 200);
 
-        cy.wrap(response!.body.max_signals).should('eql', getExistingRule().maxSignals);
-        cy.wrap(response!.body.enabled).should('eql', false);
+        cy.wrap(response?.body.max_signals).should('eql', getExistingRule().maxSignals);
+        cy.wrap(response?.body.enabled).should('eql', false);
       });
     });
 
@@ -414,9 +414,9 @@ describe('Custom detection rules deletion and edition', () => {
       saveEditedRule();
 
       cy.wait('@getRule').then(({ response }) => {
-        cy.wrap(response!.statusCode).should('eql', 200);
+        cy.wrap(response?.statusCode).should('eql', 200);
         // ensure that editing rule does not modify max_signals
-        cy.wrap(response!.body.max_signals).should('eql', getExistingRule().maxSignals);
+        cy.wrap(response?.body.max_signals).should('eql', getExistingRule().maxSignals);
       });
 
       cy.get(RULE_NAME_HEADER).should('contain', `${getEditedRule().name}`);

x-pack/plugins/security_solution/cypress/integration/detection_rules/export_rule.spec.ts

@@ -35,7 +35,7 @@ describe('Export rules', () => {
     goToManageAlertsDetectionRules();
     exportFirstRule();
     cy.wait('@export').then(({ response }) => {
-      cy.wrap(response!.body).should('eql', expectedExportedRule(this.ruleResponse));
+      cy.wrap(response?.body).should('eql', expectedExportedRule(this.ruleResponse));
     });
   });
 });

x-pack/plugins/security_solution/cypress/integration/timeline_templates/creation.spec.ts

@@ -70,7 +70,7 @@ describe('Timeline Templates', () => {
     addNameToTimeline(getTimeline().title);
 
     cy.wait('@timeline').then(({ response }) => {
-      const timelineId = response!.body.data.persistTimeline.timeline.savedObjectId;
+      const timelineId = response?.body.data.persistTimeline.timeline.savedObjectId;
 
       addDescriptionToTimeline(getTimeline().description);
       addNotesToTimeline(getTimeline().notes);

x-pack/plugins/security_solution/cypress/integration/timeline_templates/export.spec.ts

@@ -35,9 +35,9 @@ describe('Export timelines', () => {
     exportTimeline(this.templateId);
 
     cy.wait('@export').then(({ response }) => {
-      cy.wrap(response!.statusCode).should('eql', 200);
+      cy.wrap(response?.statusCode).should('eql', 200);
 
-      cy.wrap(response!.body).should(
+      cy.wrap(response?.body).should(
         'eql',
         expectedExportedTimelineTemplate(this.templateResponse)
       );

x-pack/plugins/security_solution/cypress/integration/timelines/export.spec.ts

@@ -33,9 +33,9 @@ describe('Export timelines', () => {
     exportTimeline(this.timelineId);
 
     cy.wait('@export').then(({ response }) => {
-      cy.wrap(response!.statusCode).should('eql', 200);
+      cy.wrap(response?.statusCode).should('eql', 200);
 
-      cy.wrap(response!.body).should('eql', expectedExportedTimeline(this.timelineResponse));
+      cy.wrap(response?.body).should('eql', expectedExportedTimeline(this.timelineResponse));
     });
   });
 });

x-pack/plugins/security_solution/cypress/integration/timelines/search_or_filter.spec.ts

@@ -54,17 +54,17 @@ describe('Update kqlMode for timeline', () => {
   it('should be able to update timeline kqlMode with filter', () => {
     cy.get(TIMELINE_KQLMODE_FILTER).click();
     cy.wait('@update').then(({ response }) => {
-      cy.wrap(response!.statusCode).should('eql', 200);
-      cy.wrap(response!.body.data.persistTimeline.timeline.kqlMode).should('eql', 'filter');
+      cy.wrap(response?.statusCode).should('eql', 200);
+      cy.wrap(response?.body.data.persistTimeline.timeline.kqlMode).should('eql', 'filter');
       cy.get(ADD_FILTER).should('exist');
     });
   });
 
   it('should be able to update timeline kqlMode with search', () => {
     cy.get(TIMELINE_KQLMODE_SEARCH).click();
     cy.wait('@update').then(({ response }) => {
-      cy.wrap(response!.statusCode).should('eql', 200);
-      cy.wrap(response!.body.data.persistTimeline.timeline.kqlMode).should('eql', 'search');
+      cy.wrap(response?.statusCode).should('eql', 200);
+      cy.wrap(response?.body.data.persistTimeline.timeline.kqlMode).should('eql', 'search');
       cy.get(ADD_FILTER).should('not.exist');
     });
   });

x-pack/plugins/security_solution/cypress/integration/urls/state.spec.ts

@@ -250,8 +250,8 @@ describe('url state', () => {
 
     cy.wait('@timeline').then(({ response }) => {
       closeTimeline();
-      cy.wrap(response!.statusCode).should('eql', 200);
-      const timelineId = response!.body.data.persistTimeline.timeline.savedObjectId;
+      cy.wrap(response?.statusCode).should('eql', 200);
+      const timelineId = response?.body.data.persistTimeline.timeline.savedObjectId;
       cy.visit('/app/home');
       cy.visit(`/app/security/timelines?timeline=(id:'${timelineId}',isOpen:!t)`);
       cy.get(DATE_PICKER_APPLY_BUTTON_TIMELINE).should('exist');

x-pack/plugins/security_solution/cypress/integration/value_lists/value_lists.spec.ts

@@ -174,8 +174,8 @@ describe('value lists', () => {
         cy.wait('@exportList').then(({ response }) => {
           cy.fixture(listName).then((list: string) => {
             const [lineOne, lineTwo] = list.split('\n');
-            expect(response!.body).to.contain(lineOne);
-            expect(response!.body).to.contain(lineTwo);
+            expect(response?.body).to.contain(lineOne);
+            expect(response?.body).to.contain(lineTwo);
           });
         });
       });
@@ -189,8 +189,8 @@ describe('value lists', () => {
         cy.wait('@exportList').then(({ response }) => {
           cy.fixture(listName).then((list: string) => {
             const [lineOne, lineTwo] = list.split('\n');
-            expect(response!.body).to.contain(lineOne);
-            expect(response!.body).to.contain(lineTwo);
+            expect(response?.body).to.contain(lineOne);
+            expect(response?.body).to.contain(lineTwo);
           });
         });
       });
@@ -204,8 +204,8 @@ describe('value lists', () => {
         cy.wait('@exportList').then(({ response }) => {
           cy.fixture(listName).then((list: string) => {
             const [lineOne, lineTwo] = list.split('\n');
-            expect(response!.body).to.contain(lineOne);
-            expect(response!.body).to.contain(lineTwo);
+            expect(response?.body).to.contain(lineOne);
+            expect(response?.body).to.contain(lineTwo);
           });
         });
       });
@@ -219,7 +219,7 @@ describe('value lists', () => {
         cy.wait('@exportList').then(({ response }) => {
           cy.fixture(listName).then((list: string) => {
             const [lineOne] = list.split('\n');
-            expect(response!.body).to.contain(lineOne);
+            expect(response?.body).to.contain(lineOne);
           });
         });
       });

x-pack/plugins/security_solution/cypress/screens/timelines.ts

@@ -9,7 +9,10 @@ export const BULK_ACTIONS = '[data-test-subj="utility-bar-action-button"]';
 
 export const EXPORT_TIMELINE_ACTION = '[data-test-subj="export-timeline-action"]';
 
-export const TIMELINE = (id: string) => {
+export const TIMELINE = (id: string | undefined) => {
+  if (id == null) {
+    throw new TypeError('id should never be null or undefined');
+  }
   return `[data-test-subj="title-${id}"]`;
 };
 

x-pack/plugins/security_solution/cypress/tasks/create_new_rule.ts

@@ -254,7 +254,7 @@ export const fillDefineCustomRuleWithImportedQueryAndContinue = (
   rule: CustomRule | OverrideRule
 ) => {
   cy.get(IMPORT_QUERY_FROM_SAVED_TIMELINE_LINK).click();
-  cy.get(TIMELINE(rule.timeline.id!)).click();
+  cy.get(TIMELINE(rule.timeline.id)).click();
   cy.get(CUSTOM_QUERY_INPUT).should('have.value', rule.customQuery);
   cy.get(DEFINE_CONTINUE_BUTTON).should('exist').click({ force: true });
 
@@ -273,7 +273,7 @@ export const fillDefineThresholdRule = (rule: ThresholdRule) => {
   const threshold = 1;
 
   cy.get(IMPORT_QUERY_FROM_SAVED_TIMELINE_LINK).click();
-  cy.get(TIMELINE(rule.timeline.id!)).click();
+  cy.get(TIMELINE(rule.timeline.id)).click();
   cy.get(COMBO_BOX_CLEAR_BTN).first().click();
 
   rule.index.forEach((index) => {
@@ -298,7 +298,7 @@ export const fillDefineThresholdRuleAndContinue = (rule: ThresholdRule) => {
     cy.wrap($el).type(rule.thresholdField, { delay: 35 });
 
   cy.get(IMPORT_QUERY_FROM_SAVED_TIMELINE_LINK).click();
-  cy.get(TIMELINE(rule.timeline.id!)).click();
+  cy.get(TIMELINE(rule.timeline.id)).click();
   cy.get(CUSTOM_QUERY_INPUT).should('have.value', rule.customQuery);
   cy.get(THRESHOLD_INPUT_AREA)
     .find(INPUT)
@@ -314,9 +314,12 @@ export const fillDefineThresholdRuleAndContinue = (rule: ThresholdRule) => {
 };
 
 export const fillDefineEqlRuleAndContinue = (rule: CustomRule) => {
+  if (rule.customQuery == null) {
+    throw new TypeError('The rule custom query should never be undefined or null ');
+  }
   cy.get(RULES_CREATION_FORM).find(EQL_QUERY_INPUT).should('exist');
   cy.get(RULES_CREATION_FORM).find(EQL_QUERY_INPUT).should('be.visible');
-  cy.get(RULES_CREATION_FORM).find(EQL_QUERY_INPUT).type(rule.customQuery!);
+  cy.get(RULES_CREATION_FORM).find(EQL_QUERY_INPUT).type(rule.customQuery);
   cy.get(RULES_CREATION_FORM).find(EQL_QUERY_VALIDATION_SPINNER).should('not.exist');
   cy.get(RULES_CREATION_PREVIEW)
     .find(QUERY_PREVIEW_BUTTON)

x-pack/plugins/security_solution/cypress/tasks/login.ts

@@ -57,7 +57,7 @@ const LOGIN_API_ENDPOINT = '/internal/security/login';
  */
 export const getUrlWithRoute = (role: ROLES, route: string) => {
   const url = Cypress.config().baseUrl;
-  const kibana = new URL(url!);
+  const kibana = new URL(String(url));
   const theUrl = `${Url.format({
     auth: `${role}:changeme`,
     username: role,
@@ -83,7 +83,7 @@ interface User {
  */
 export const constructUrlWithUser = (user: User, route: string) => {
   const url = Cypress.config().baseUrl;
-  const kibana = new URL(url!);
+  const kibana = new URL(String(url));
   const hostname = kibana.hostname;
   const username = user.username;
   const password = user.password;

x-pack/plugins/security_solution/cypress/tasks/rule_details.ts

@@ -32,7 +32,7 @@ export const activatesRule = () => {
   cy.get(RULE_SWITCH).should('be.visible');
   cy.get(RULE_SWITCH).click();
   cy.wait('@bulk_update').then(({ response }) => {
-    cy.wrap(response!.statusCode).should('eql', 200);
+    cy.wrap(response?.statusCode).should('eql', 200);
   });
 };
 

x-pack/plugins/security_solution/public/common/components/charts/barchart.tsx

@@ -94,7 +94,7 @@ export const BarChartBaseComponent = ({
             yAccessors={yAccessors}
             timeZone={timeZone}
             splitSeriesAccessors={splitSeriesAccessors}
-            data={series.value!}
+            data={series.value ?? []}
             stackAccessors={get('configs.series.stackAccessors', chartConfigs)}
             color={series.color ? series.color : undefined}
           />

x-pack/plugins/security_solution/public/common/components/event_details/helpers.test.tsx

@@ -12,7 +12,7 @@ import { mockBrowserFields } from '../../containers/source/mock';
 
 const aField = {
   ...mockDetailItemData[4],
-  ...mockBrowserFields.base.fields!['@timestamp'],
+  ...mockBrowserFields.base.fields?.['@timestamp'],
 };
 
 describe('helpers', () => {

x-pack/plugins/security_solution/public/common/components/event_details/helpers.tsx

@@ -127,7 +127,7 @@ export const getColumnsWithTimestamp = ({
 export const getExampleText = (example: string | number | null | undefined): string =>
   !isEmpty(example) ? `Example: ${example}` : '';
 
-export const getIconFromType = (type: string | null) => {
+export const getIconFromType = (type: string | null | undefined) => {
   switch (type) {
     case 'string': // fall through
     case 'keyword':

x-pack/plugins/security_solution/public/common/components/events_viewer/events_viewer.tsx

@@ -236,7 +236,7 @@ const EventsViewerComponent: React.FC<Props> = ({
     useTimelineEvents({
       docValueFields,
       fields,
-      filterQuery: combinedQueries!.filterQuery,
+      filterQuery: combinedQueries?.filterQuery,
       id,
       indexNames,
       limit: itemsPerPage,
@@ -300,7 +300,7 @@ const EventsViewerComponent: React.FC<Props> = ({
               height={headerFilterGroup ? COMPACT_HEADER_HEIGHT : EVENTS_VIEWER_HEADER_HEIGHT}
               subtitle={utilityBar ? undefined : subtitle}
               title={globalFullScreen ? titleWithExitFullScreen : justTitle}
-              isInspectDisabled={combinedQueries!.filterQuery === undefined}
+              isInspectDisabled={combinedQueries?.filterQuery === undefined}
             >
               {HeaderSectionContent}
             </HeaderSection>