Fix #244 by returning null if no icon is found

Author: michaelspiss

util/lib/main.dart

@@ -285,8 +285,8 @@ to complete successfully.
     '/// name starting with `fa-`. Should multiple classes fulfill these',
     '/// requirements, the first occurrence is chosen.',
     '/// ',
-    '/// Returns [FontAwesomeIcons.circleQuestion] if no icon matches.',
-    'IconData getIconFromCss(String cssClasses) {',
+    '/// Returns null if no icon matches.',
+    'IconData? getIconFromCss(String cssClasses) {',
     '  const Map<String, String> cssStyles = {',
     "    'far': 'regular', 'fas': 'solid', 'fab': 'brands',",
     "    'fad': 'duotone', 'fal': 'light', 'fat': 'thin',",
@@ -303,7 +303,7 @@ to complete successfully.
     '',
     "  return faIconNameMapping[style + ' ' + icon] ?? FontAwesomeIcons.circleQuestion;",
     '  } on StateError {',
-    '  return FontAwesomeIcons.circleQuestion;',
+    '  return null;',
     '  }',
     '}',
     '',