有没有办法只向TextFormField中的labelText添加填充？

import 'package:flutter/material.dart';

class CustomTextFormField extends FormField<String> {
  CustomTextFormField({
    Key? key,
    TextEditingController? controller,
    String? labelText,
    FormFieldValidator<String>? validator,
  }) : super(
          key: key,
          initialValue: controller?.text,
          validator: validator,
          builder: (FormFieldState<String> field) {
            final InputDecoration decoration = InputDecoration(
              labelText: labelText,
              errorText: field.errorText,
              contentPadding: EdgeInsets.symmetric(vertical: 10.0),
            );

            return Container(
              padding: EdgeInsets.symmetric(horizontal: 10.0),
              child: TextFormField(
                controller: controller,
                decoration: decoration,
                onChanged: field.didChange,
                validator: validator,
              ),
            );
          },
        );
}

CustomTextFormField(
  controller: _textEditingController,
  labelText: 'Username',
  validator: (value) {
    if (value == null || value.isEmpty) {
      return 'Please enter your username';
    }
    return null;
  },
)