Merge pull request #80 from team-gogo/fix/student-by-id-api-spec

[internal] 학생 정보 인터널 API 스펙 수정

Author: vumrra

src/main/kotlin/gogo/gogostage/global/internal/student/stub/StudentStub.kt

@@ -9,7 +9,7 @@ data class StudentByIdStub(
     val schoolId: Long,
     val email: String,
     val name: String,
-    val deviceToken: String,
+    val deviceToken: String?,
     val sex: Sex,
     val classNumber: Int,
     val studentNumber: Int,