User_Role composite key: add NotNull constraint annotation

Signed-off-by: Pekka Helenius <fincer89@hotmail.com>

bookstore/src/main/java/com/fjordtek/bookstore/model/auth/UserRoleCompositeKey.java

@@ -6,6 +6,7 @@ import java.io.Serializable;
 import java.util.Objects;
 
 import javax.persistence.Embeddable;
+import javax.validation.constraints.NotNull;
 
 /**
  * This class implements a composite primary key based on
@@ -21,8 +22,9 @@ public class UserRoleCompositeKey implements Serializable {
 
 	private static final long serialVersionUID = 2889337731246989510L;
 
+	@NotNull
 	private Long userId;
-
+	@NotNull
 	private Long roleId;
 
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