Add nullish coalesce checks, touch up specs

app/assets/javascripts/jobs/store/utils.js

@@ -132,13 +132,11 @@ export const logLinesParserLegacy = (lines = [], accumulator = []) =>
   );
 
 export const logLinesParser = (lines = [], previousTraceState = {}, prevParsedLines = []) => {
-  let currentLine = previousTraceState?.prevLineCount ? previousTraceState.prevLineCount : 0;
-  let currentHeader = previousTraceState?.currentHeader ? previousTraceState.currentHeader : null;
-  let isPreviousLineHeader = previousTraceState?.isPreviousLineHeader
-    ? previousTraceState.isPreviousLineHeader
-    : false;
+  let currentLine = previousTraceState?.prevLineCount ?? 0;
+  let currentHeader = previousTraceState?.currentHeader;
+  let isPreviousLineHeader = previousTraceState?.isPreviousLineHeader ?? false;
   const parsedLines = prevParsedLines.length > 0 ? prevParsedLines : [];
-  const sectionsQueue = previousTraceState?.sectionsQueue ? previousTraceState.sectionsQueue : [];
+  const sectionsQueue = previousTraceState?.sectionsQueue ?? [];
 
   for (let i = 0; i < lines.length; i += 1) {
     const line = lines[i];

spec/frontend/jobs/components/log/log_spec.js

@@ -84,7 +84,7 @@ describe('Job Log', () => {
   });
 });
 
-describe('Job Log, feature flag enabled', () => {
+describe('Job Log, infinitelyCollapsibleSections feature flag enabled', () => {
   let wrapper;
   let actions;
   let state;

spec/frontend/jobs/store/mutations_spec.js

@@ -323,7 +323,7 @@ describe('Job Store mutations, feature flag ON', () => {
           });
         });
 
-        describe('when it is defined', () => {
+        describe('when lines are defined', () => {
           it('sets the parsed log ', () => {
             mutations[types.RECEIVE_TRACE_SUCCESS](stateCopy, {
               append: false,
@@ -344,7 +344,7 @@ describe('Job Store mutations, feature flag ON', () => {
           });
         });
 
-        describe('when it is null', () => {
+        describe('when lines are null', () => {
           it('sets the default value', () => {
             mutations[types.RECEIVE_TRACE_SUCCESS](stateCopy, {
               append: true,