diff --git a/src/main/java/com/inteligr8/alfresco/activiti/model/HistoricProcessInstanceQueryRepresentation.java b/src/main/java/com/inteligr8/alfresco/activiti/model/HistoricProcessInstanceQueryRepresentation.java
index 176b943..c73c606 100644
--- a/src/main/java/com/inteligr8/alfresco/activiti/model/HistoricProcessInstanceQueryRepresentation.java
+++ b/src/main/java/com/inteligr8/alfresco/activiti/model/HistoricProcessInstanceQueryRepresentation.java
@@ -3,7 +3,7 @@
 package com.inteligr8.alfresco.activiti.model;
 
 import java.time.OffsetDateTime;
-import java.util.ArrayList;
+import java.util.LinkedList;
 import java.util.List;
 
 import com.fasterxml.jackson.annotation.JsonInclude;
@@ -39,15 +39,15 @@ import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 public class HistoricProcessInstanceQueryRepresentation {
 
     @JsonProperty("excludeSubprocesses")
-    private boolean excludeSubprocesses;
+    private Boolean excludeSubprocesses;
     @JsonProperty("finished")
-    private boolean finished;
+    private Boolean finished;
     @JsonProperty("finishedAfter")
     private OffsetDateTime finishedAfter;
     @JsonProperty("finishedBefore")
     private OffsetDateTime finishedBefore;
     @JsonProperty("includeProcessVariables")
-    private boolean includeProcessVariables;
+    private Boolean includeProcessVariables;
     @JsonProperty("involvedUser")
     private String involvedUser;
     @JsonProperty("order")
@@ -63,11 +63,11 @@ public class HistoricProcessInstanceQueryRepresentation {
     @JsonProperty("processInstanceIds")
     private List<String> processInstanceIds;
     @JsonProperty("size")
-    private int size;
+    private Integer size;
     @JsonProperty("sort")
     private String sort;
     @JsonProperty("start")
-    private int start;
+    private Integer start;
     @JsonProperty("startedAfter")
     private OffsetDateTime startedAfter;
     @JsonProperty("startedBefore")
@@ -81,9 +81,9 @@ public class HistoricProcessInstanceQueryRepresentation {
     @JsonProperty("tenantIdLike")
     private String tenantIdLike;
     @JsonProperty("variables")
-    private List<QueryVariable> variables = new ArrayList<QueryVariable>();
+    private List<QueryVariable> variables;
     @JsonProperty("withoutTenantId")
-    private boolean withoutTenantId;
+    private Boolean withoutTenantId;
 
     /**
      * No args constructor for use in serialization
@@ -91,28 +91,28 @@ public class HistoricProcessInstanceQueryRepresentation {
     public HistoricProcessInstanceQueryRepresentation() {
     }
 
-    public boolean isExcludeSubprocesses() {
+    public Boolean isExcludeSubprocesses() {
         return excludeSubprocesses;
     }
 
-    public void setExcludeSubprocesses(boolean excludeSubprocesses) {
+    public void setExcludeSubprocesses(Boolean excludeSubprocesses) {
         this.excludeSubprocesses = excludeSubprocesses;
     }
 
-    public HistoricProcessInstanceQueryRepresentation withExcludeSubprocesses(boolean excludeSubprocesses) {
+    public HistoricProcessInstanceQueryRepresentation withExcludeSubprocesses(Boolean excludeSubprocesses) {
         this.excludeSubprocesses = excludeSubprocesses;
         return this;
     }
 
-    public boolean isFinished() {
+    public Boolean isFinished() {
         return finished;
     }
 
-    public void setFinished(boolean finished) {
+    public void setFinished(Boolean finished) {
         this.finished = finished;
     }
 
-    public HistoricProcessInstanceQueryRepresentation withFinished(boolean finished) {
+    public HistoricProcessInstanceQueryRepresentation withFinished(Boolean finished) {
         this.finished = finished;
         return this;
     }
@@ -143,15 +143,15 @@ public class HistoricProcessInstanceQueryRepresentation {
         return this;
     }
 
-    public boolean isIncludeProcessVariables() {
+    public Boolean isIncludeProcessVariables() {
         return includeProcessVariables;
     }
 
-    public void setIncludeProcessVariables(boolean includeProcessVariables) {
+    public void setIncludeProcessVariables(Boolean includeProcessVariables) {
         this.includeProcessVariables = includeProcessVariables;
     }
 
-    public HistoricProcessInstanceQueryRepresentation withIncludeProcessVariables(boolean includeProcessVariables) {
+    public HistoricProcessInstanceQueryRepresentation withIncludeProcessVariables(Boolean includeProcessVariables) {
         this.includeProcessVariables = includeProcessVariables;
         return this;
     }
@@ -247,15 +247,15 @@ public class HistoricProcessInstanceQueryRepresentation {
         return this;
     }
 
-    public int getSize() {
+    public Integer getSize() {
         return size;
     }
 
-    public void setSize(int size) {
+    public void setSize(Integer size) {
         this.size = size;
     }
 
-    public HistoricProcessInstanceQueryRepresentation withSize(int size) {
+    public HistoricProcessInstanceQueryRepresentation withSize(Integer size) {
         this.size = size;
         return this;
     }
@@ -273,15 +273,15 @@ public class HistoricProcessInstanceQueryRepresentation {
         return this;
     }
 
-    public int getStart() {
+    public Integer getStart() {
         return start;
     }
 
-    public void setStart(int start) {
+    public void setStart(Integer start) {
         this.start = start;
     }
 
-    public HistoricProcessInstanceQueryRepresentation withStart(int start) {
+    public HistoricProcessInstanceQueryRepresentation withStart(Integer start) {
         this.start = start;
         return this;
     }
@@ -365,6 +365,8 @@ public class HistoricProcessInstanceQueryRepresentation {
     }
 
     public List<QueryVariable> getVariables() {
+    	if (variables == null)
+    		variables = new LinkedList<>();
         return variables;
     }
 
@@ -377,15 +379,15 @@ public class HistoricProcessInstanceQueryRepresentation {
         return this;
     }
 
-    public boolean isWithoutTenantId() {
+    public Boolean isWithoutTenantId() {
         return withoutTenantId;
     }
 
-    public void setWithoutTenantId(boolean withoutTenantId) {
+    public void setWithoutTenantId(Boolean withoutTenantId) {
         this.withoutTenantId = withoutTenantId;
     }
 
-    public HistoricProcessInstanceQueryRepresentation withWithoutTenantId(boolean withoutTenantId) {
+    public HistoricProcessInstanceQueryRepresentation withWithoutTenantId(Boolean withoutTenantId) {
         this.withoutTenantId = withoutTenantId;
         return this;
     }
diff --git a/src/main/java/com/inteligr8/alfresco/activiti/model/ProcessInstanceQueryRepresentation.java b/src/main/java/com/inteligr8/alfresco/activiti/model/ProcessInstanceQueryRepresentation.java
index dce3fe8..2949b2c 100644
--- a/src/main/java/com/inteligr8/alfresco/activiti/model/ProcessInstanceQueryRepresentation.java
+++ b/src/main/java/com/inteligr8/alfresco/activiti/model/ProcessInstanceQueryRepresentation.java
@@ -40,17 +40,17 @@ public class ProcessInstanceQueryRepresentation {
     }
 
     @JsonProperty("appDefinitionId")
-    private long appDefinitionId;
+    private Long appDefinitionId;
     @JsonProperty("processDefinitionId")
     private String processDefinitionId;
     @JsonProperty("processInstanceId")
     private String processInstanceId;
     @JsonProperty("size")
-    private int size;
+    private Integer size;
     @JsonProperty("sort")
     private Sort sort;
     @JsonProperty("start")
-    private int start;
+    private Integer start;
     @JsonProperty("state")
     private State state;
 
@@ -60,15 +60,15 @@ public class ProcessInstanceQueryRepresentation {
     public ProcessInstanceQueryRepresentation() {
     }
 
-    public long getAppDefinitionId() {
+    public Long getAppDefinitionId() {
         return appDefinitionId;
     }
 
-    public void setAppDefinitionId(long appDefinitionId) {
+    public void setAppDefinitionId(Long appDefinitionId) {
         this.appDefinitionId = appDefinitionId;
     }
 
-    public ProcessInstanceQueryRepresentation withAppDefinitionId(long appDefinitionId) {
+    public ProcessInstanceQueryRepresentation withAppDefinitionId(Long appDefinitionId) {
         this.appDefinitionId = appDefinitionId;
         return this;
     }
@@ -99,15 +99,15 @@ public class ProcessInstanceQueryRepresentation {
         return this;
     }
 
-    public int getSize() {
+    public Integer getSize() {
         return size;
     }
 
-    public void setSize(int size) {
+    public void setSize(Integer size) {
         this.size = size;
     }
 
-    public ProcessInstanceQueryRepresentation withSize(int size) {
+    public ProcessInstanceQueryRepresentation withSize(Integer size) {
         this.size = size;
         return this;
     }
@@ -125,15 +125,15 @@ public class ProcessInstanceQueryRepresentation {
         return this;
     }
 
-    public int getStart() {
+    public Integer getStart() {
         return start;
     }
 
-    public void setStart(int start) {
+    public void setStart(Integer start) {
         this.start = start;
     }
 
-    public ProcessInstanceQueryRepresentation withStart(int start) {
+    public ProcessInstanceQueryRepresentation withStart(Integer start) {
         this.start = start;
         return this;
     }