Flutter ElevatedButton设置onPressed为null后不显示问题求助

我编写了一个支持多种样式与状态的自定义按钮组件，代码如下：

import 'package:flutter/material.dart';

import '../common/texts.dart';
import '../common/colors.dart';

enum ButtonVariant { primary, secondary, text }

enum ButtonState { enabled, disabled, loading }

class CustomButton extends StatelessWidget {
  final String text;
  final ButtonVariant variant;
  final ButtonState state;
  final VoidCallback? onPressed;

  const CustomButton({
    super.key,
    required this.text,
    this.variant = ButtonVariant.primary,
    this.state = ButtonState.enabled,
    this.onPressed,
  });

  @override
  Widget build(BuildContext context) {
    Color backgroundColor;
    Color textColor;

    switch (variant) {
      case ButtonVariant.primary:
        backgroundColor = green500;
        textColor = black;
        break;
      case ButtonVariant.secondary:
        backgroundColor = Colors.blue;
        textColor = Colors.white;
        break;
      case ButtonVariant.text:
        backgroundColor = Colors.transparent;
        textColor = Colors.blue;
        break;
    }

    if (state == ButtonState.disabled) {
      backgroundColor = backgroundColor.withOpacity(0.5);
      textColor = textColor.withOpacity(0.5);
    }

    return ElevatedButton(
      style: ElevatedButton.styleFrom(
        backgroundColor: backgroundColor,
        foregroundColor: textColor,
        padding: const EdgeInsets.symmetric(vertical: 16.0, horizontal: 24.0),
        shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.circular(22),
        ),
      ),
      onPressed: state == ButtonState.disabled ? null : onPressed,
      child: state == ButtonState.loading
          ? CircularProgressIndicator(
              valueColor: AlwaysStoppedAnimation<Color>(textColor),
            )
          : Text(text, style: caption2Black),
    );
  }
}

按照官方预期，ElevatedButton 的 onPressed 设为 null 时应进入禁用状态，但在我的场景中，按钮会直接消失不见。

当我将代码中的：

onPressed: state == ButtonState.disabled ? null : onPressed,

修改为：

onPressed: state == ButtonState.disabled ? () {} : onPressed,

后，按钮就能正常显示（见下图），点击时也能触发标准的渐隐按压动画。

有没有人遇到过类似问题？我尝试了多种方法都无法解决。我的运行环境：
Flutter (Channel stable, 3.13.3, on macOS 14.5 23F79 darwin-x64, locale en-DE)

内容的提问来源于stack exchange，提问作者Ala Ha