elective master - detail student query error fixed

src/views/elective/generation/detail.vue

@@ -213,6 +213,7 @@ export default {
         this.detailWrapper = res.data
 
         const studentIds = res.data.details?.map(d => d['studentId']).toString()
+        if (!studentIds) return Promise.resolve({ data: {} })
         return getGenerationOptionalMajorsBatch({ studentIds })
       }).then(res => {
         this.majorsMap = res.data