fixed bug in JPA implementation: "save" methods were implemented using "merge" instead of "persist"

src/main/java/org/springframework/samples/petclinic/repository/jpa/JpaOwnerRepositoryImpl.java

@@ -70,7 +70,7 @@ public class JpaOwnerRepositoryImpl implements OwnerRepository {
 
     @Override
     public void save(Owner owner) {
-        this.em.merge(owner);
+        this.em.persist(owner);
 
     }
 

src/main/java/org/springframework/samples/petclinic/repository/jpa/JpaPetRepositoryImpl.java

@@ -53,7 +53,7 @@ public class JpaPetRepositoryImpl implements PetRepository {
 
     @Override
     public void save(Pet pet) {
-        this.em.merge(pet);
+        this.em.persist(pet);
     }
 
 }

src/main/java/org/springframework/samples/petclinic/repository/jpa/JpaVisitRepositoryImpl.java

@@ -45,7 +45,7 @@ public class JpaVisitRepositoryImpl implements VisitRepository {
 
     @Override
     public void save(Visit visit) {
-        this.em.merge(visit);
+        this.em.persist(visit);
     }