Add getFontSize function

lib/src/utils/font.dart

@@ -0,0 +1,18 @@
+double getFontSize(dynamic sizeValue) {
+  if (sizeValue.value is double) {
+    return sizeValue;
+  }
+
+  if (sizeValue is int) {
+    return sizeValue.toDouble();
+  }
+
+  double? fontSize;
+  if (sizeValue is String) {
+    fontSize = double.tryParse(sizeValue);
+    if (fontSize == null) {
+      throw 'Invalid size $sizeValue';
+    }
+  }
+  return fontSize!;
+}

lib/src/widgets/text_line.dart

@@ -17,6 +17,7 @@ import '../models/documents/nodes/line.dart';
 import '../models/documents/nodes/node.dart';
 import '../models/documents/style.dart';
 import '../utils/color.dart';
+import '../utils/font.dart';
 import '../utils/platform.dart';
 import 'box.dart';
 import 'controller.dart';
@@ -342,19 +343,7 @@ class _TextLineState extends State<TextLine> {
           res = res.merge(defaultStyles.sizeHuge);
           break;
         default:
-          double? fontSize;
-          if (size.value is double) {
-            fontSize = size.value;
-          } else if (size.value is int) {
-            fontSize = size.value.toDouble();
-          } else if (size.value is String) {
-            fontSize = double.tryParse(size.value);
-          }
-          if (fontSize != null) {
-            res = res.merge(TextStyle(fontSize: fontSize));
-          } else {
-            throw 'Invalid size ${size.value}';
-          }
+          res = res.merge(TextStyle(fontSize: getFontSize(size.value)));
       }
     }