fixed null-array read bug

src/views/elective/report/components/major-introduce-batch.vue

@@ -28,7 +28,7 @@ export default {
   },
   computed: {
     majors() {
-      const all = this.getOptionalMajors()
+      const all = this.getOptionalMajors() || []
       if (!all.length) return []
       const distinctMajors = {}
       all.forEach(item => {