diff --git a/src/main/java/com/example/cosmos_serversb/models/Groups.java b/src/main/java/com/example/cosmos_serversb/models/Groups.java
index 1b145a1..757ada5 100644
--- a/src/main/java/com/example/cosmos_serversb/models/Groups.java
+++ b/src/main/java/com/example/cosmos_serversb/models/Groups.java
@@ -50,6 +50,9 @@
     }
 
     public static Group createGroup(String name, String uId){
+        if(name == null || uId == null){
+            return null; //not-null制約
+        }
         User user = getUserById(uId);
         if(user == null){
             return null; //存在しないユーザがグループを作成しようとした。
@@ -163,6 +166,9 @@
     }
 
     public static Request addRequests(String gId, String uId, String product, String deadline, int location){
+        if(product == null){
+            return null; //not-null制約
+        }
         String rId = getInstance().createRId();
         String uri = baseURI + AppName + "/groups/" + gId + "/requests/" + rId;
         Request request = new Request(rId, uri, new Date(), uId, product, deadline, location);
@@ -190,6 +196,9 @@
     }
 
     public static Request updateRequest(String gId, String rId, String uId, String product, String deadline, int location, boolean done){
+        if(product ==  null){
+            return null; //not-null制約
+        }
         Session session = SessionManager.getInstance().getSession();
         Request editRequest = session.get(Request.class, rId);
         if(editRequest != null){
diff --git a/src/main/java/com/example/cosmos_serversb/models/Users.java b/src/main/java/com/example/cosmos_serversb/models/Users.java
index a2d4b8a..10342f7 100644
--- a/src/main/java/com/example/cosmos_serversb/models/Users.java
+++ b/src/main/java/com/example/cosmos_serversb/models/Users.java
@@ -68,6 +68,9 @@
     }
 
     public static User createUser(String name, String pw, String iconImage) {
+        if(name == null || pw == null){
+            return null; //not-null制約
+        }
         String uId = getInstance().createUId();
         String uri = baseURI + AppName +"/users/" +uId;
 
@@ -92,6 +95,9 @@
          * 
          * TODO: checkPasswordメソッドを用いパスワードを確認する
          */
+        if(name == null || pw == null){
+            return null; //not-null制約
+        }
         Session session = SessionManager.getInstance().getSession();
         List usersList = session.createQuery( "from User" ).list();
         List passwordList = session.createQuery("from Password").list();