diff --git a/src/main/java/eu/openaire/urls_controller/models/Assignment.java b/src/main/java/eu/openaire/urls_controller/models/Assignment.java
index 211243c..bd5b216 100644
--- a/src/main/java/eu/openaire/urls_controller/models/Assignment.java
+++ b/src/main/java/eu/openaire/urls_controller/models/Assignment.java
@@ -1,21 +1,35 @@
 package eu.openaire.urls_controller.models;
 
+import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 
 import java.util.Date;
 import java.util.List;
 
 
+@JsonInclude(JsonInclude.Include.NON_NULL)
+@JsonPropertyOrder({
+        "tasks",
+        "workerId",
+        "date"
+})
 public class Assignment {
 
     @JsonProperty("tasks")
-    List<Task> tasks;
+    private List<Task> tasks;
 
     @JsonProperty("workerId")
-    String workerId;
+    private String workerId;
 
     @JsonProperty("date")
-    Date date;
+    private Date date;
+
+    public Assignment(List<Task> tasks, String workerId, Date date) {
+        this.tasks = tasks;
+        this.workerId = workerId;
+        this.date = date;
+    }
 
     public List<Task> getTasks() {
         return tasks;
diff --git a/src/main/java/eu/openaire/urls_controller/models/Error.java b/src/main/java/eu/openaire/urls_controller/models/Error.java
index 45a4ed5..3edc6b0 100644
--- a/src/main/java/eu/openaire/urls_controller/models/Error.java
+++ b/src/main/java/eu/openaire/urls_controller/models/Error.java
@@ -1,14 +1,21 @@
 package eu.openaire.urls_controller.models;
 
+import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 
+@JsonInclude(JsonInclude.Include.NON_NULL)
+@JsonPropertyOrder({
+        "type",
+        "message"
+})
 public class Error {
 
     @JsonProperty("type")
-    String type;
+    private String type;
 
     @JsonProperty("message")
-    String message;
+    private String message;
 
     public String getType() {
         return type;
diff --git a/src/main/java/eu/openaire/urls_controller/models/Payload.java b/src/main/java/eu/openaire/urls_controller/models/Payload.java
index 7a985e0..6d39c35 100644
--- a/src/main/java/eu/openaire/urls_controller/models/Payload.java
+++ b/src/main/java/eu/openaire/urls_controller/models/Payload.java
@@ -27,7 +27,7 @@ public class Payload {
     private String original_url;
 
     @JsonProperty("actual_url")
-    private String actual_url;
+    private String actual_url;  // The url of the full-text itself.
 
     @JsonProperty("date_acquired")
     private String date_acquired;
@@ -51,6 +51,14 @@ public class Payload {
     private String provenance;
 
 
+    public String getId() {
+        return id;
+    }
+
+    public void setId(String id) {
+        this.id = id;
+    }
+
     public String getOriginal_url() {
         return original_url;
     }
@@ -123,15 +131,6 @@ public class Payload {
         this.provenance = provenance;
     }
 
-
-    public String getId() {
-        return id;
-    }
-
-    public void setId(String id) {
-        this.id = id;
-    }
-
     @Override
     public String toString() {
         return "Payload{" +
diff --git a/src/main/java/eu/openaire/urls_controller/models/Publication.java b/src/main/java/eu/openaire/urls_controller/models/Publication.java
index ff07db6..bbd4372 100644
--- a/src/main/java/eu/openaire/urls_controller/models/Publication.java
+++ b/src/main/java/eu/openaire/urls_controller/models/Publication.java
@@ -14,11 +14,9 @@ import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 })
 public class Publication {
 
-
     @JsonProperty("id")
     private String id;
 
-
     @JsonProperty("dedupid")
     private String dedupid;
 
diff --git a/src/main/java/eu/openaire/urls_controller/models/Task.java b/src/main/java/eu/openaire/urls_controller/models/Task.java
index 9446ee4..ff56b4f 100644
--- a/src/main/java/eu/openaire/urls_controller/models/Task.java
+++ b/src/main/java/eu/openaire/urls_controller/models/Task.java
@@ -1,14 +1,26 @@
 package eu.openaire.urls_controller.models;
 
+import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 
+@JsonInclude(JsonInclude.Include.NON_NULL)
+@JsonPropertyOrder({
+        "id",
+        "url"
+})
 public class Task {
 
     @JsonProperty("id")
-    String id;
+    private String id;
 
     @JsonProperty("url")
-    String url;
+    private String url;
+
+    public Task(String id, String url) {
+        this.id = id;
+        this.url = url;
+    }
 
     public String getId() {
         return id;
diff --git a/src/main/java/eu/openaire/urls_controller/models/UrlToCheck.java b/src/main/java/eu/openaire/urls_controller/models/UrlToCheck.java
index b674404..5bf6700 100644
--- a/src/main/java/eu/openaire/urls_controller/models/UrlToCheck.java
+++ b/src/main/java/eu/openaire/urls_controller/models/UrlToCheck.java
@@ -13,15 +13,12 @@ import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 })
 public class UrlToCheck {  // This model will not match with a database,
 
-
     @JsonProperty("id")
     private String id;
 
-
     @JsonProperty("url")
     private String url;
 
-
     public UrlToCheck() {
     }
 
diff --git a/src/main/java/eu/openaire/urls_controller/payloads/requests/UrlsRequest.java b/src/main/java/eu/openaire/urls_controller/payloads/requests/UrlsRequest.java
index 0db124b..e9b81f7 100644
--- a/src/main/java/eu/openaire/urls_controller/payloads/requests/UrlsRequest.java
+++ b/src/main/java/eu/openaire/urls_controller/payloads/requests/UrlsRequest.java
@@ -1,11 +1,16 @@
 package eu.openaire.urls_controller.payloads.requests;
 
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonProperty;
 import eu.openaire.urls_controller.models.Payload;
 
 import java.util.List;
 
+
+@JsonInclude(JsonInclude.Include.NON_NULL)
 public class UrlsRequest {
 
+    @JsonProperty("payloads")
     private List<Payload> payloads;
 
     public void UrlsResponse() {