diff --git a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Driver.java b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Driver.java
index 9802d5c..ff1e142 100644
--- a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Driver.java
+++ b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Driver.java
@@ -3,7 +3,6 @@ package dst.ass1.jpa.model.impl;
 import dst.ass1.jpa.model.*;
 
 import javax.persistence.*;
-import javax.validation.constraints.NotNull;
 import java.util.ArrayList;
 import java.util.Collection;
 
@@ -16,7 +15,7 @@ public class Driver extends PlatformUser implements IDriver {
     private IVehicle vehicle;
 
     @OneToMany(targetEntity = Employment.class)
-    private Collection<IEmployment> employments;
+    private Collection<IEmployment> employments = new ArrayList<>();
 
     @Override
     public Collection<IEmployment> getEmployments() {
diff --git a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Employment.java b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Employment.java
index b913f01..46d49e9 100644
--- a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Employment.java
+++ b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Employment.java
@@ -14,8 +14,11 @@ import static dst.ass1.jpa.util.Constants.T_ORGANIZATION;
 
 @Entity
 public class Employment implements IEmployment {
-    @EmbeddedId @Target(EmploymentKey.class) private IEmploymentKey id;
+    @EmbeddedId @Target(EmploymentKey.class)
+    private IEmploymentKey id;
+
     private Date since;
+
     private Boolean active;
 
     @MapsId(T_ORGANIZATION)
diff --git a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Location.java b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Location.java
index 6f99c53..d348817 100644
--- a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Location.java
+++ b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Location.java
@@ -4,16 +4,20 @@ import dst.ass1.jpa.model.ILocation;
 import dst.ass1.jpa.model.ITrip;
 
 import javax.persistence.*;
+import java.util.ArrayList;
 import java.util.Collection;
 
 @Entity
 public class Location implements ILocation {
-    @Id @GeneratedValue private Long id;
+    @Id @GeneratedValue
+    private Long id;
+
     private String name;
+
     private Long locationId;
 
     @ManyToMany(targetEntity = Trip.class)
-    private Collection<ITrip> trips;
+    private Collection<ITrip> trips = new ArrayList<>();
 
     @Override
     public Long getId() {
diff --git a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Match.java b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Match.java
index f013997..81cdb03 100644
--- a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Match.java
+++ b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Match.java
@@ -7,9 +7,13 @@ import java.util.Date;
 
 @Entity
 public class Match implements IMatch {
-    @Id @GeneratedValue private Long id;
+    @Id @GeneratedValue
+    private Long id;
+
     private Date date;
-    @Embedded private IMoney fare;
+
+    @Embedded
+    private IMoney fare;
 
     @OneToOne(targetEntity = Trip.class)
     private ITrip trip;
diff --git a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/ModelFactory.java b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/ModelFactory.java
index 1e8803e..c145eb0 100644
--- a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/ModelFactory.java
+++ b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/ModelFactory.java
@@ -6,7 +6,6 @@ import dst.ass1.jpa.model.*;
  * Creates new instances of your model implementations.
  */
 public class ModelFactory implements IModelFactory {
-
     @Override
     public IModelFactory createModelFactory() {
         return new ModelFactory();
diff --git a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Money.java b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Money.java
index 2c853ca..659d56e 100644
--- a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Money.java
+++ b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Money.java
@@ -8,6 +8,7 @@ import java.math.BigDecimal;
 @Embeddable
 public class Money implements IMoney {
     private String currency;
+
     private BigDecimal value;
 
     @Override
diff --git a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Organization.java b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Organization.java
index 83619ca..63a32fd 100644
--- a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Organization.java
+++ b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Organization.java
@@ -5,13 +5,16 @@ import dst.ass1.jpa.model.IOrganization;
 import dst.ass1.jpa.model.IVehicle;
 
 import javax.persistence.*;
+import java.util.ArrayList;
 import java.util.Collection;
 
 import static dst.ass1.jpa.util.Constants.*;
 
 @Entity
 public class Organization implements IOrganization {
-    @Id @GeneratedValue private Long id;
+    @Id @GeneratedValue
+    private Long id;
+
     private String name;
 
     @ManyToMany(targetEntity = Organization.class)
@@ -20,16 +23,16 @@ public class Organization implements IOrganization {
             joinColumns = @JoinColumn(name = I_ORGANIZATION_PART_OF),
             inverseJoinColumns = @JoinColumn(name = I_ORGANIZATION_PARTS)
     )
-    private Collection<IOrganization> parts;
+    private Collection<IOrganization> parts = new ArrayList<>();
 
     @ManyToMany(mappedBy = "parts", targetEntity = Organization.class)
-    private Collection<IOrganization> partOf;
+    private Collection<IOrganization> partOf = new ArrayList<>();
 
     @ManyToMany(targetEntity = Vehicle.class)
-    private Collection<IVehicle> vehicles;
+    private Collection<IVehicle> vehicles = new ArrayList<>();
 
     @OneToMany(targetEntity = Employment.class)
-    private Collection<IEmployment> employments;
+    private Collection<IEmployment> employments = new ArrayList<>();
 
     public Organization() {
     }
diff --git a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Preferences.java b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Preferences.java
index 57287bc..39d67c3 100644
--- a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Preferences.java
+++ b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Preferences.java
@@ -4,17 +4,22 @@ import dst.ass1.jpa.model.IPreferences;
 import dst.ass1.jpa.model.IRider;
 
 import javax.persistence.*;
+import java.util.HashMap;
 import java.util.Map;
 
+import static dst.ass1.jpa.util.Constants.*;
+
 @Entity
 public class Preferences implements IPreferences {
-    @Id
+    @Id @GeneratedValue
     private Long id;
-    @ElementCollection
-    private Map<String, String> data;
 
-    @OneToOne(fetch = FetchType.LAZY)
-    @MapsId
+    @ElementCollection(fetch = FetchType.LAZY)
+    @OrderColumn
+    @JoinTable(name = J_PREFERENCES_DATA)
+    private Map<String, String> data = new HashMap<>();
+
+    @OneToOne(targetEntity = Rider.class, fetch = FetchType.LAZY)
     private IRider rider;
 
     @Override
diff --git a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Rider.java b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Rider.java
index 2af5cee..ac7b948 100644
--- a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Rider.java
+++ b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Rider.java
@@ -6,6 +6,7 @@ import dst.ass1.jpa.model.ITrip;
 
 import javax.persistence.*;
 import javax.validation.constraints.NotNull;
+import java.util.ArrayList;
 import java.util.Collection;
 
 import static dst.ass1.jpa.util.Constants.M_RIDER_ACCOUNT;
diff --git a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Trip.java b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Trip.java
index 5bf1b08..34f3c94 100644
--- a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Trip.java
+++ b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Trip.java
@@ -3,6 +3,7 @@ package dst.ass1.jpa.model.impl;
 import dst.ass1.jpa.model.*;
 
 import javax.persistence.*;
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Date;
 
@@ -10,11 +11,19 @@ import static dst.ass1.jpa.util.Constants.*;
 
 @Entity
 public class Trip implements ITrip {
-    @Id @GeneratedValue private Long id;
+    @Id @GeneratedValue
+    private Long id;
+
     private Date created;
+
     private Date updated;
+
     private TripState state;
+
+    @OneToOne(targetEntity = Location.class, optional = false)
     private ILocation pickup;
+
+    @OneToOne(targetEntity = Location.class, optional = false)
     private ILocation destination;
 
     @ManyToMany(targetEntity = Location.class)
@@ -23,10 +32,15 @@ public class Trip implements ITrip {
             joinColumns = @JoinColumn(name = I_TRIP),
             inverseJoinColumns = @JoinColumn(name = I_LOCATION)
     )
-    private Collection<ILocation> stops;
+    private Collection<ILocation> stops = new ArrayList<>();
 
+    @OneToOne(targetEntity = TripInfo.class)
     private ITripInfo tripInfo;
+
+    @OneToOne(targetEntity = Match.class)
     private IMatch match;
+
+    @OneToOne(targetEntity = Rider.class)
     private IRider rider;
 
     @Override
diff --git a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/TripInfo.java b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/TripInfo.java
index 0a2b6f0..48060a0 100644
--- a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/TripInfo.java
+++ b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/TripInfo.java
@@ -4,21 +4,23 @@ import dst.ass1.jpa.model.IMoney;
 import dst.ass1.jpa.model.ITrip;
 import dst.ass1.jpa.model.ITripInfo;
 
-import javax.persistence.Embedded;
-import javax.persistence.Entity;
-import javax.persistence.Id;
-import javax.persistence.OneToOne;
+import javax.persistence.*;
 import java.util.Date;
 
 @Entity
 public class TripInfo implements ITripInfo {
-   @Id
+   @Id @GeneratedValue
    private Long id;
+
    private Date completed;
+
    private Double distance;
+
    @Embedded
    private IMoney total;
+
    private Integer driverRating;
+
    private Integer riderRating;
 
    @OneToOne(targetEntity = Trip.class)
diff --git a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Vehicle.java b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Vehicle.java
index d2fa945..74729cd 100644
--- a/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Vehicle.java
+++ b/ass1-jpa/src/main/java/dst/ass1/jpa/model/impl/Vehicle.java
@@ -10,17 +10,22 @@ import java.util.Collection;
 
 @Entity
 public class Vehicle implements IVehicle {
-    @Id
+    @Id @GeneratedValue
     private Long id;
+
     @Column(unique = true)
     private String license;
+
     private String color;
+
     private String type;
 
     @OneToMany(targetEntity = Driver.class)
     private Collection<IDriver> driver;
+
     @OneToMany(targetEntity = Match.class)
     private Collection<IMatch> match;
+
     @ManyToMany(mappedBy = "vehicles", targetEntity = Organization.class)
     private Collection<IOrganization> organization;