Use isValid instead of isNull and add a test for gpkg

src/app/qgisapp.cpp

@@ -4611,7 +4611,7 @@ bool QgisApp::addVectorLayers( const QStringList &layerQStringList, const QStrin
       // Try to extract the database name and use it as base name
       // sublayers names (if any) will be appended to the layer name
       auto parts( QgsProviderRegistry::instance()->decodeUri( QStringLiteral( "ogr" ), src ) );
-      if ( ! parts.value( QStringLiteral( "layerName" ) ).isNull() )
+      if ( parts.value( QStringLiteral( "layerName" ) ).isValid() )
         baseName = parts.value( QStringLiteral( "layerName" ) ).toString();
       else
         baseName = src;

tests/src/providers/testqgsogrprovider.cpp

@@ -126,6 +126,8 @@ void TestQgsOgrProvider::decodeUri()
   QCOMPARE( parts.value( QStringLiteral( "layerName" ) ).toString(), QString( "database_name" ) );
   parts = QgsProviderRegistry::instance()->decodeUri( QStringLiteral( "ogr" ), QStringLiteral( "MYSQL:westholland,user=root,password=psv9570,port=3306,tables=bedrijven" ) );
   QCOMPARE( parts.value( QStringLiteral( "layerName" ) ).toString(), QString( "westholland" ) );
+  parts = QgsProviderRegistry::instance()->decodeUri( QStringLiteral( "ogr" ), QStringLiteral( "/path/to/a/geopackage.gpkg|layername=a_layer" ) );
+  QCOMPARE( parts.value( QStringLiteral( "layerName" ) ).toString(), QString( "a_layer" ) );
 }