diff --git a/app/src/main/java/com/example/tampopo_client/viewmodels/ActivityViewModel.java b/app/src/main/java/com/example/tampopo_client/viewmodels/ActivityViewModel.java
index 979f251..3d15caf 100644
--- a/app/src/main/java/com/example/tampopo_client/viewmodels/ActivityViewModel.java
+++ b/app/src/main/java/com/example/tampopo_client/viewmodels/ActivityViewModel.java
@@ -13,8 +13,8 @@
 import java.time.format.DateTimeFormatter;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.HashMap;
 import java.util.Comparator;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.SortedSet;
@@ -147,7 +147,7 @@
 
         List<Activity> userActivities = userActivitiesLiveData.getValue();
 
-        if (userActivities.isEmpty()) {
+        if (userActivities == null || userActivities.isEmpty()) {
             userActivitiesLiveData.postValue(List.of(latestActivity));
         } else {
             if (userActivities.equals(List.of(latestActivity))) {
@@ -304,7 +304,7 @@
      * @return 取得対象のユーザーのアクティビティのリストのライブデータ
      */
     public MutableLiveData<List<Activity>> getActivitiesLiveDataFromUserId(String userId) {
-        if(!friendToActivitiesLiveData.containsKey(userId)){
+        if (!friendToActivitiesLiveData.containsKey(userId)) {
             friendToActivitiesLiveData.put(userId, new MutableLiveData<>());
         }
         return friendToActivitiesLiveData.get(userId);