Revert changes in _SelectHeaderStyleButtonState

lib/widgets/text_line.dart

@@ -60,7 +60,7 @@ class TextLine extends StatelessWidget {
         textAlign,
         textDirection,
         1.0,
-        Localizations.localeOf(context),
+        Localizations.localeOf(context, nullOk: true),
         strutStyle,
         TextWidthBasis.parent,
         null);

lib/widgets/toolbar.dart

@@ -446,13 +446,7 @@ Widget _selectHeadingStyleButtonBuilder(
     height: iconSize * 1.77,
     fillColor: Theme.of(context).canvasColor,
     child: Text(
-      _valueToText[value.key == "header"
+      _valueToText[value],
-          ? Attribute.header
-          : (value.key == "h1")
-              ? Attribute.h1
-              : (value.key == "h2")
-                  ? Attribute.h2
-                  : Attribute.h3],
       style: TextStyle(fontSize: 13, fontWeight: FontWeight.w600),
     ),
     initialValue: value,