diff --git a/gui/include/Visualization/VisualizationGraphWidget.h b/gui/include/Visualization/VisualizationGraphWidget.h
index 74b34ed..33998b0 100644
--- a/gui/include/Visualization/VisualizationGraphWidget.h
+++ b/gui/include/Visualization/VisualizationGraphWidget.h
@@ -3,12 +3,15 @@
 
 #include "Visualization/IVisualizationWidget.h"
 
+#include <QLoggingCategory>
 #include <QWidget>
 
 #include <memory>
 
 #include <Common/spimpl.h>
 
+Q_DECLARE_LOGGING_CATEGORY(LOG_VisualizationGraphWidget)
+
 class Variable;
 
 namespace Ui {
diff --git a/gui/include/Visualization/VisualizationTabWidget.h b/gui/include/Visualization/VisualizationTabWidget.h
index ac5a39d..2adcb91 100644
--- a/gui/include/Visualization/VisualizationTabWidget.h
+++ b/gui/include/Visualization/VisualizationTabWidget.h
@@ -5,8 +5,11 @@
 
 #include <Common/spimpl.h>
 
+#include <QLoggingCategory>
 #include <QWidget>
 
+Q_DECLARE_LOGGING_CATEGORY(LOG_VisualizationTabWidget)
+
 class Variable;
 class VisualizationZoneWidget;
 
diff --git a/gui/include/Visualization/VisualizationWidget.h b/gui/include/Visualization/VisualizationWidget.h
index 4e0dbe5..52285c2 100644
--- a/gui/include/Visualization/VisualizationWidget.h
+++ b/gui/include/Visualization/VisualizationWidget.h
@@ -6,11 +6,11 @@
 #include <QLoggingCategory>
 #include <QWidget>
 
+Q_DECLARE_LOGGING_CATEGORY(LOG_VisualizationWidget)
+
 class Variable;
 class VisualizationTabWidget;
 
-Q_DECLARE_LOGGING_CATEGORY(LOG_VisualizationWidget)
-
 namespace Ui {
 class VisualizationWidget;
 } // namespace Ui
diff --git a/gui/include/Visualization/VisualizationZoneWidget.h b/gui/include/Visualization/VisualizationZoneWidget.h
index b6bafaf..9aa4a78 100644
--- a/gui/include/Visualization/VisualizationZoneWidget.h
+++ b/gui/include/Visualization/VisualizationZoneWidget.h
@@ -3,8 +3,11 @@
 
 #include "Visualization/IVisualizationWidget.h"
 
+#include <QLoggingCategory>
 #include <QWidget>
 
+Q_DECLARE_LOGGING_CATEGORY(LOG_VisualizationZoneWidget)
+
 namespace Ui {
 class VisualizationZoneWidget;
 } // Ui
diff --git a/gui/src/Visualization/VisualizationGraphWidget.cpp b/gui/src/Visualization/VisualizationGraphWidget.cpp
index 7f8ebd9..ee02cb7 100644
--- a/gui/src/Visualization/VisualizationGraphWidget.cpp
+++ b/gui/src/Visualization/VisualizationGraphWidget.cpp
@@ -7,6 +7,8 @@
 
 #include <unordered_map>
 
+Q_LOGGING_CATEGORY(LOG_VisualizationGraphWidget, "VisualizationGraphWidget")
+
 namespace {
 
 /// Key pressed to enable zoom on horizontal axis
@@ -62,6 +64,10 @@ void VisualizationGraphWidget::accept(IVisualizationWidgetVisitor *visitor)
     if (visitor) {
         visitor->visit(this);
     }
+    else {
+        qCCritical(LOG_VisualizationGraphWidget())
+            << tr("Can't visit widget : the visitor is null");
+    }
 }
 
 bool VisualizationGraphWidget::canDrop(const Variable &variable) const
diff --git a/gui/src/Visualization/VisualizationTabWidget.cpp b/gui/src/Visualization/VisualizationTabWidget.cpp
index 69825a9..bfa0d6a 100644
--- a/gui/src/Visualization/VisualizationTabWidget.cpp
+++ b/gui/src/Visualization/VisualizationTabWidget.cpp
@@ -4,6 +4,8 @@
 
 #include "Visualization/VisualizationZoneWidget.h"
 
+Q_LOGGING_CATEGORY(LOG_VisualizationTabWidget, "VisualizationTabWidget")
+
 namespace {
 
 /// Generates a default name for a new zone, according to the number of zones already displayed in
@@ -78,6 +80,9 @@ void VisualizationTabWidget::accept(IVisualizationWidgetVisitor *visitor)
 
         visitor->visitLeave(this);
     }
+    else {
+        qCCritical(LOG_VisualizationTabWidget()) << tr("Can't visit widget : the visitor is null");
+    }
 }
 
 bool VisualizationTabWidget::canDrop(const Variable &variable) const
diff --git a/gui/src/Visualization/VisualizationWidget.cpp b/gui/src/Visualization/VisualizationWidget.cpp
index 4e65d64..65a7fee 100644
--- a/gui/src/Visualization/VisualizationWidget.cpp
+++ b/gui/src/Visualization/VisualizationWidget.cpp
@@ -97,6 +97,9 @@ void VisualizationWidget::accept(IVisualizationWidgetVisitor *visitor)
 
         visitor->visitLeave(this);
     }
+    else {
+        qCCritical(LOG_VisualizationWidget()) << tr("Can't visit widget : the visitor is null");
+    }
 }
 
 bool VisualizationWidget::canDrop(const Variable &variable) const
diff --git a/gui/src/Visualization/VisualizationZoneWidget.cpp b/gui/src/Visualization/VisualizationZoneWidget.cpp
index ae4e841..75970ce 100644
--- a/gui/src/Visualization/VisualizationZoneWidget.cpp
+++ b/gui/src/Visualization/VisualizationZoneWidget.cpp
@@ -4,6 +4,8 @@
 
 #include "Visualization/VisualizationGraphWidget.h"
 
+Q_LOGGING_CATEGORY(LOG_VisualizationZoneWidget, "VisualizationZoneWidget")
+
 namespace {
 
 /// Generates a default name for a new graph, according to the number of graphs already displayed in
@@ -73,6 +75,9 @@ void VisualizationZoneWidget::accept(IVisualizationWidgetVisitor *visitor)
 
         visitor->visitLeave(this);
     }
+    else {
+        qCCritical(LOG_VisualizationZoneWidget()) << tr("Can't visit widget : the visitor is null");
+    }
 }
 
 bool VisualizationZoneWidget::canDrop(const Variable &variable) const