MoritzMoreira · Jul 26, 2025 · Jul 26, 2025 · Oct 21, 2026 · Oct 27, 2026 · Oct 29, 2026
diff --git a/python/PyQt6/core/auto_additions/qgsfieldformatter.py b/python/PyQt6/core/auto_additions/qgsfieldformatter.py
@@ -2,6 +2,8 @@
 QgsFieldFormatter.CanProvideAvailableValues = QgsFieldFormatter.Flag.CanProvideAvailableValues
 QgsFieldFormatter.Flags = lambda flags=0: QgsFieldFormatter.Flag(flags)
 try:
+    QgsFieldFormatter.__attribute_docs__ = {'NULL_VALUE': "Will be saved in the configuration when a value is NULL.\nIt's the magic UUID {2839923C-8B7D-419E-B84B-CA2FE9B80EC7}"}
+    QgsFieldFormatter.__annotations__ = {'NULL_VALUE': str}
     QgsFieldFormatter.__virtual_methods__ = ['representValue', 'sortValue', 'alignmentFlag', 'createCache', 'availableValues']
     QgsFieldFormatter.__abstract_methods__ = ['id']
 except (NameError, AttributeError):

diff --git a/python/PyQt6/core/auto_additions/qgsvaluemapfieldformatter.py b/python/PyQt6/core/auto_additions/qgsvaluemapfieldformatter.py
@@ -1,7 +1,5 @@
 # The following has been generated automatically from src/core/fieldformatter/qgsvaluemapfieldformatter.h
 try:
-    QgsValueMapFieldFormatter.__attribute_docs__ = {'NULL_VALUE': "Will be saved in the configuration when a value is NULL.\nIt's the magic UUID {2839923C-8B7D-419E-B84B-CA2FE9B80EC7}"}
-    QgsValueMapFieldFormatter.__annotations__ = {'NULL_VALUE': str}
     QgsValueMapFieldFormatter.__overridden_methods__ = ['id', 'representValue', 'sortValue', 'availableValues']
     QgsValueMapFieldFormatter.__group__ = ['fieldformatter']
 except (NameError, AttributeError):

diff --git a/python/PyQt6/core/auto_generated/fieldformatter/qgsvaluemapfieldformatter.sip.in b/python/PyQt6/core/auto_generated/fieldformatter/qgsvaluemapfieldformatter.sip.in
@@ -32,8 +32,6 @@ the above configuration:
 #include "qgsvaluemapfieldformatter.h"
 %End
   public:
-    static const QString NULL_VALUE;
-
     QgsValueMapFieldFormatter();
 %Docstring
 Default constructor of field formatter for a value map field.

diff --git a/python/PyQt6/core/auto_generated/qgsfieldformatter.sip.in b/python/PyQt6/core/auto_generated/qgsfieldformatter.sip.in
@@ -57,6 +57,8 @@ This is an abstract base class and will always need to be subclassed.
 #include "qgsfieldformatter.h"
 %End
   public:
+    static const QString NULL_VALUE;
+
     QgsFieldFormatter();
 
     virtual ~QgsFieldFormatter();

diff --git a/python/PyQt6/gui/auto_generated/editorwidgets/core/qgseditorwidgetwrapper.sip.in b/python/PyQt6/gui/auto_generated/editorwidgets/core/qgseditorwidgetwrapper.sip.in
@@ -238,6 +238,16 @@ Controls if the constraint result should be visualized on the widget
                                 (mostly editable status)
 %End
 
+    void updateComboBoxValues( const QVariant &value, QComboBox *comboBox );
+%Docstring
+Adds a value to the combobox, for example the default value or the value
+from :py:func:`QgsEditorWidgetWrapper.setValues()`. Updates the combobox
+to show the new value.
+
+:param value: The new value of the attribute
+:param comboBox: Pointer to the combobox of the widget
+%End
+
   signals:
 
  void valueChanged( const QVariant &value );

diff --git a/src/core/fieldformatter/qgsvaluemapfieldformatter.cpp b/src/core/fieldformatter/qgsvaluemapfieldformatter.cpp
@@ -22,8 +22,6 @@
 
 using namespace Qt::StringLiterals;
 
-const QString QgsValueMapFieldFormatter::NULL_VALUE = u"{2839923C-8B7D-419E-B84B-CA2FE9B80EC7}"_s;
-
 QgsValueMapFieldFormatter::QgsValueMapFieldFormatter()
 {
   setFlags( flags() | QgsFieldFormatter::CanProvideAvailableValues );

diff --git a/src/core/fieldformatter/qgsvaluemapfieldformatter.h b/src/core/fieldformatter/qgsvaluemapfieldformatter.h
@@ -41,12 +41,6 @@
 class CORE_EXPORT QgsValueMapFieldFormatter : public QgsFieldFormatter
 {
   public:
-    /**
-     * Will be saved in the configuration when a value is NULL.
-     * It's the magic UUID {2839923C-8B7D-419E-B84B-CA2FE9B80EC7}
-     */
-    static const QString NULL_VALUE;
-
     /**
       * Default constructor of field formatter for a value map field.
       */

diff --git a/src/core/qgsfieldformatter.cpp b/src/core/qgsfieldformatter.cpp
@@ -21,6 +21,12 @@
 #include "qgsvectordataprovider.h"
 #include "qgsvectorlayer.h"
 
+#include <QString>
+
+using namespace Qt::StringLiterals;
+
+const QString QgsFieldFormatter::NULL_VALUE = u"{2839923C-8B7D-419E-B84B-CA2FE9B80EC7}"_s;
+
 QString QgsFieldFormatter::representValue( QgsVectorLayer *layer, int fieldIndex, const QVariantMap &config, const QVariant &cache, const QVariant &value ) const
 {
   Q_UNUSED( config )

diff --git a/src/core/qgsfieldformatter.h b/src/core/qgsfieldformatter.h
@@ -67,6 +67,12 @@ class CORE_EXPORT QgsFieldFormatterContext
 class CORE_EXPORT QgsFieldFormatter
 {
   public:
+    /**
+     * Will be saved in the configuration when a value is NULL.
+     * It's the magic UUID {2839923C-8B7D-419E-B84B-CA2FE9B80EC7}
+     */
+    static const QString NULL_VALUE;
+
     QgsFieldFormatter() = default;
 
     virtual ~QgsFieldFormatter() = default;

diff --git a/src/gui/attributeformconfig/qgsattributetypedialog.cpp b/src/gui/attributeformconfig/qgsattributetypedialog.cpp
@@ -619,12 +619,12 @@ void QgsAttributeTypeDialog::defaultExpressionChanged()
     return;
   }
 
-  const QVariant val = exp.evaluate( &context );
   if ( exp.hasEvalError() )
   {
     mDefaultPreviewLabel->setText( "<i>" + exp.evalErrorString() + "</i>" );
     return;
   }
+  const QVariant val = exp.evaluate( &context );
 
   // if the expression uses fields and it's not on update,
   // there is no warranty that the field will be available

diff --git a/src/gui/editorwidgets/core/qgseditorwidgetwrapper.cpp b/src/gui/editorwidgets/core/qgseditorwidgetwrapper.cpp
@@ -15,11 +15,11 @@
 
 #include "qgseditorwidgetwrapper.h"
 
+#include "qgsapplication.h"
+#include "qgsfieldformatter.h"
 #include "qgsfields.h"
 #include "qgsvectordataprovider.h"
 #include "qgsvectorlayer.h"
-#include "qgsvectorlayerjoinbuffer.h"
-#include "qgsvectorlayerjoininfo.h"
 #include "qgsvectorlayerutils.h"
 
 #include <QString>
@@ -32,6 +32,8 @@ using namespace Qt::StringLiterals;
 QgsEditorWidgetWrapper::QgsEditorWidgetWrapper( QgsVectorLayer *vl, int fieldIdx, QWidget *editor, QWidget *parent )
   : QgsWidgetWrapper( vl, editor, parent )
   , mFieldIdx( fieldIdx )
+  , mValidConstraint( true )
+  , mIsBlockingCommit( false )
 {}
 
 int QgsEditorWidgetWrapper::fieldIdx() const
@@ -158,6 +160,26 @@ void QgsEditorWidgetWrapper::updateValues( const QVariant &value, const QVariant
   Q_NOWARN_DEPRECATED_POP
 }
 
+void QgsEditorWidgetWrapper::updateComboBoxValues( const QVariant &value, QComboBox *comboBox )
+{
+  if ( comboBox )
+  {
+    if ( !QgsVariantUtils::isNull( value ) )
+    {
+      QString v = value.toString();
+      if ( comboBox->findData( v ) == -1 )
+      {
+        comboBox->addItem( v.prepend( '(' ).append( ')' ), v );
+      }
+    }
+    // The null value is added only when allow null is checked
+    else if ( config( u"AllowNull"_s ).toBool() && comboBox->findData( QgsFieldFormatter::NULL_VALUE ) == -1 )
+    {
+      comboBox->addItem( QgsApplication::nullRepresentation().prepend( '(' ).append( ')' ), QgsFieldFormatter::NULL_VALUE );
+    }
+  }
+}
+
 QgsEditorWidgetWrapper::ConstraintResult QgsEditorWidgetWrapper::constraintResult() const
 {
   return mConstraintResult;

diff --git a/src/gui/editorwidgets/core/qgseditorwidgetwrapper.h b/src/gui/editorwidgets/core/qgseditorwidgetwrapper.h
@@ -18,6 +18,7 @@
 
 #include "qgis_sip.h"
 
+#include <QComboBox>
 #include <QMap>
 #include <QObject>
 #include <QVariant>
@@ -235,6 +236,15 @@ class GUI_EXPORT QgsEditorWidgetWrapper : public QgsWidgetWrapper
      */
     void setConstraintResultVisible( bool constraintResultVisible );
 
+    /**
+    * Adds a value to the combobox, for example the default value or the value from QgsEditorWidgetWrapper::setValues().
+    * Updates the combobox to show the new value.
+    *
+    * \param value The new value of the attribute
+    * \param comboBox Pointer to the combobox of the widget
+    */
+    void updateComboBoxValues( const QVariant &value, QComboBox *comboBox );
+
   signals:
 
     /**

diff --git a/src/gui/editorwidgets/qgsuniquevaluesconfigdlg.cpp b/src/gui/editorwidgets/qgsuniquevaluesconfigdlg.cpp
@@ -15,6 +15,8 @@
 
 #include "qgsuniquevaluesconfigdlg.h"
 
+#include "qgsproject.h"
+
 #include <QString>
 
 #include "moc_qgsuniquevaluesconfigdlg.cpp"
@@ -26,6 +28,7 @@ QgsUniqueValuesConfigDlg::QgsUniqueValuesConfigDlg( QgsVectorLayer *vl, int fiel
 {
   setupUi( this );
   connect( editableUniqueValues, &QAbstractButton::toggled, this, &QgsEditorConfigWidget::changed );
+  connect( allowNullCheckBox, &QAbstractButton::toggled, this, &QgsEditorConfigWidget::changed );
 }
 
 
@@ -34,11 +37,21 @@ QVariantMap QgsUniqueValuesConfigDlg::config()
   QVariantMap cfg;
 
   cfg.insert( u"Editable"_s, editableUniqueValues->isChecked() );
+  cfg.insert( u"AllowNull"_s, allowNullCheckBox->isChecked() );
 
   return cfg;
 }
 
 void QgsUniqueValuesConfigDlg::setConfig( const QVariantMap &config )
 {
   editableUniqueValues->setChecked( config.value( u"Editable"_s, false ).toBool() );
+
+  QSet<QVariant> uniqueValues = layer()->uniqueValues( field() );
+  if ( config.value( u"AllowNull"_s ).isNull() )
+  {
+    bool uniqueValuesContainNull = uniqueValues.contains( QVariant( QgsVariantUtils::createNullVariant( layer()->fields().at( field() ).type() ) ) );
+    allowNullCheckBox->setChecked( uniqueValuesContainNull );
+  }
+  else
+    allowNullCheckBox->setChecked( config.value( u"AllowNull"_s ).toBool() );
 }
diff --git a/src/gui/editorwidgets/qgsuniquevaluewidgetwrapper.cpp b/src/gui/editorwidgets/qgsuniquevaluewidgetwrapper.cpp
@@ -16,6 +16,7 @@
 #include "qgsuniquevaluewidgetwrapper.h"
 
 #include "qgsapplication.h"
+#include "qgsfieldformatter.h"
 #include "qgsfilterlineedit.h"
 #include "qgsvectorlayer.h"
 
@@ -77,7 +78,10 @@ void QgsUniqueValuesWidgetWrapper::initWidget( QWidget *editor )
   {
     if ( mComboBox )
     {
-      mComboBox->addItem( v.toString(), v );
+      if ( v != QgsVariantUtils::createNullVariant( layer()->fields().at( fieldIdx() ).type() ) )
+      {
+        mComboBox->addItem( v.toString(), v );
+      }
     }
 
     if ( mLineEdit )
@@ -132,16 +136,12 @@ void QgsUniqueValuesWidgetWrapper::showIndeterminateState()
 
 void QgsUniqueValuesWidgetWrapper::updateValues( const QVariant &value, const QVariantList & )
 {
-  if ( mComboBox )
-  {
-    mComboBox->setCurrentIndex( mComboBox->findData( value ) );
-  }
-
-  if ( mLineEdit )
+  QSet<QVariant> uniqueValues = layer()->uniqueValues( fieldIdx() );
+  bool uniqueValuesContainNull = uniqueValues.contains( QgsVariantUtils::createNullVariant( layer()->fields().at( fieldIdx() ).type() ) );
+  // Add a null value when the layer was created in an older QGIS version, and the field contains a null value
+  if ( uniqueValuesContainNull && config( u"AllowNull"_s ).isNull() )
   {
-    if ( QgsVariantUtils::isNull( value ) )
-      mLineEdit->setText( QgsApplication::nullRepresentation() );
-    else
-      mLineEdit->setText( value.toString() );
+    mComboBox->addItem( QgsApplication::nullRepresentation().prepend( '(' ).append( ')' ), QgsFieldFormatter::NULL_VALUE );
   }
+  updateComboBoxValues( value, mComboBox );
 }
diff --git a/src/gui/editorwidgets/qgsvaluemapconfigdlg.cpp b/src/gui/editorwidgets/qgsvaluemapconfigdlg.cpp
@@ -17,8 +17,8 @@
 
 #include "qgsapplication.h"
 #include "qgsattributetypeloaddialog.h"
+#include "qgsfieldformatter.h"
 #include "qgssettings.h"
-#include "qgsvaluemapfieldformatter.h"
 
 #include <QClipboard>
 #include <QFileDialog>
@@ -69,7 +69,7 @@ QVariantMap QgsValueMapConfigDlg::config()
 
     QString ks = ki->text();
     if ( ( ks == QgsApplication::nullRepresentation() ) && !( ki->flags() & Qt::ItemIsEditable ) )
-      ks = QgsValueMapFieldFormatter::NULL_VALUE;
+      ks = QgsFieldFormatter::NULL_VALUE;
 
     QVariantMap value;
 
@@ -134,7 +134,7 @@ void QgsValueMapConfigDlg::vCellChanged( int row, int column )
   {
     // check cell value
     QTableWidgetItem *item = tableWidget->item( row, 0 );
-    if ( item && item->data( Qt::ItemDataRole::UserRole ) != QgsValueMapFieldFormatter::NULL_VALUE )
+    if ( item && item->data( Qt::ItemDataRole::UserRole ) != QgsFieldFormatter::NULL_VALUE )
     {
       const QString validValue = checkValueLength( item->text() );
       if ( validValue.length() != item->text().length() )
@@ -200,7 +200,7 @@ void QgsValueMapConfigDlg::updateMap( const QList<QPair<QString, QVariant>> &lis
 
   if ( insertNull )
   {
-    setRow( row, QgsValueMapFieldFormatter::NULL_VALUE, u"<NULL>"_s );
+    setRow( row, QgsFieldFormatter::NULL_VALUE, u"<NULL>"_s );
     ++row;
   }
 
@@ -246,7 +246,7 @@ void QgsValueMapConfigDlg::updateMap( const QList<QPair<QString, QVariant>> &lis
 
 QString QgsValueMapConfigDlg::checkValueLength( const QString &value )
 {
-  if ( value == QgsValueMapFieldFormatter::NULL_VALUE || value == QgsApplication::nullRepresentation() )
+  if ( value == QgsFieldFormatter::NULL_VALUE || value == QgsApplication::nullRepresentation() )
   {
     return value;
   }
@@ -272,7 +272,7 @@ void QgsValueMapConfigDlg::populateComboBox( QComboBox *comboBox, const QVariant
     {
       const QVariantMap valueMap = value.toMap();
 
-      if ( skipNull && valueMap.constBegin().value() == QgsValueMapFieldFormatter::NULL_VALUE )
+      if ( skipNull && valueMap.constBegin().value() == QgsFieldFormatter::NULL_VALUE )
         continue;
 
       comboBox->addItem( valueMap.constBegin().key(), valueMap.constBegin().value() );
@@ -283,7 +283,7 @@ void QgsValueMapConfigDlg::populateComboBox( QComboBox *comboBox, const QVariant
     const QVariantMap map = config.value( u"map"_s ).toMap();
     for ( auto it = map.constBegin(); it != map.constEnd(); ++it )
     {
-      if ( skipNull && it.value() == QgsValueMapFieldFormatter::NULL_VALUE )
+      if ( skipNull && it.value() == QgsFieldFormatter::NULL_VALUE )
         continue;
 
       comboBox->addItem( it.key(), it.value() );
@@ -312,12 +312,12 @@ void QgsValueMapConfigDlg::setRow( int row, const QString &value, const QString
   QTableWidgetItem *valueCell = nullptr;
   QTableWidgetItem *descriptionCell = new QTableWidgetItem( description );
   tableWidget->insertRow( row );
-  if ( value == QgsValueMapFieldFormatter::NULL_VALUE )
+  if ( value == QgsFieldFormatter::NULL_VALUE )
   {
     QFont cellFont;
     cellFont.setItalic( true );
     valueCell = new QTableWidgetItem( QgsApplication::nullRepresentation() );
-    valueCell->setData( Qt::ItemDataRole::UserRole, QgsValueMapFieldFormatter::NULL_VALUE );
+    valueCell->setData( Qt::ItemDataRole::UserRole, QgsFieldFormatter::NULL_VALUE );
     valueCell->setFont( cellFont );
     valueCell->setFlags( Qt::ItemIsSelectable | Qt::ItemIsEnabled );
     descriptionCell->setFont( cellFont );
@@ -359,7 +359,7 @@ void QgsValueMapConfigDlg::copySelectionToClipboard()
 
 void QgsValueMapConfigDlg::addNullButtonPushed()
 {
-  setRow( tableWidget->rowCount() - 1, QgsValueMapFieldFormatter::NULL_VALUE, u"<NULL>"_s );
+  setRow( tableWidget->rowCount() - 1, QgsFieldFormatter::NULL_VALUE, u"<NULL>"_s );
 }
 
 void QgsValueMapConfigDlg::loadFromLayerButtonPushed()
@@ -413,7 +413,7 @@ void QgsValueMapConfigDlg::loadMapFromCSV( const QString &filePath )
     QString key = ceils[0];
     QString val = ceils[1];
     if ( key == QgsApplication::nullRepresentation() )
-      key = QgsValueMapFieldFormatter::NULL_VALUE;
+      key = QgsFieldFormatter::NULL_VALUE;
     map.append( qMakePair( key, val ) );
   }
 

diff --git a/src/gui/editorwidgets/qgsvaluemapwidgetwrapper.cpp b/src/gui/editorwidgets/qgsvaluemapwidgetwrapper.cpp
@@ -16,8 +16,8 @@
 #include "qgsvaluemapwidgetwrapper.h"
 
 #include "qgsapplication.h"
+#include "qgsfieldformatter.h"
 #include "qgsvaluemapconfigdlg.h"
-#include "qgsvaluemapfieldformatter.h"
 
 #include <QSettings>
 
@@ -38,7 +38,7 @@ QVariant QgsValueMapWidgetWrapper::value() const
     v = mComboBox->currentData();
   }
 
-  if ( v == QgsValueMapFieldFormatter::NULL_VALUE )
+  if ( v == QgsFieldFormatter::NULL_VALUE )
     v = QgsVariantUtils::createNullVariant( field().type() );
 
   return v;
@@ -81,7 +81,7 @@ void QgsValueMapWidgetWrapper::updateValues( const QVariant &value, const QVaria
 {
   QString v;
   if ( QgsVariantUtils::isNull( value ) )
-    v = QgsValueMapFieldFormatter::NULL_VALUE;
+    v = QgsFieldFormatter::NULL_VALUE;
   else
     v = value.toString();