[Backend] Add null checks to students.ts and add a util function `key…

…sOf`

services/backend/src/services/students.ts

@@ -91,6 +91,7 @@ const byStudentNumber = async (studentNumber: string) => {
       },
     }),
   ])
+  if (!student) return null
   const tagprogrammes = await ElementDetail.findAll({
     where: {
       code: {
@@ -324,6 +325,7 @@ const formatStudentWithoutTags = (
 export const withStudentNumber = async (studentNumber: string) => {
   try {
     const student = await byStudentNumber(studentNumber)
+    if (!student) return null
     return formatStudent(student)
   } catch (error) {
     logger.error(`Error when fetching single student ${error}`)

services/backend/src/services/studyProgramme/studyTrackStats.ts

@@ -2,6 +2,7 @@ import moment from 'moment'
 
 import { Credit, SISStudyRight, SISStudyRightElement } from '../../models'
 import { GenderCode, EnrollmentType, ExtentCode } from '../../types'
+import { keysOf } from '../../util'
 import { countTimeCategories } from '../graduationHelpers'
 import { getSemestersAndYears } from '../semesters'
 import { getDateOfFirstSemesterPresent } from './studyProgrammeBasics'
@@ -375,7 +376,7 @@ const getMainStatsByTrackAndYear = async (
         yearlyStats.Total[track] = getEmptyYear()
       }
 
-      for (const field of Object.keys(yearlyStats[year][track]) as Array<keyof (typeof yearlyStats)[string][string]>) {
+      for (const field of keysOf(yearlyStats[year][track])) {
         if (field !== 'otherCountriesCounts') {
           yearlyStats.Total[track][field] += yearlyStats[year][track][field]
           continue

services/backend/src/util/index.ts

@@ -46,3 +46,11 @@ export const sortByProgrammeCode = (a: string, b: string) => {
   }
   return a.localeCompare(b)
 }
+
+/**
+ * Returns the keys of the given object as an array of strings, typed as the keys of the object.
+ * @param obj The object whose keys are to be returned.
+ */
+export const keysOf = <T extends object>(obj: T) => {
+  return Object.keys(obj) as Array<keyof T>
+}