Widget nameField() {
    if (widget.isSignUpPage == true) {
          return Column(
            children: [
              AppTextFormField(
                hint: 'Name',
                validator: (value) {
                  if (value == null || value.isEmpty || value.startsWith(' ')) {    
                return 'Please enter a valid name';
                  }
                },
                controller: nameController,
              ),
              Gap(18.h),
            ],
          );
        }
        return const SizedBox.shrink();
}

You can get the full code from here

https://github.com/MoazSayed7/Flutter-Animated-Auth-Screens-Firebase-Login-SignUp-Reset-SignWithGoogle .

FAILURE: Build failed with an exception.    
* What went wrong:    
A problem occurred configuring project ':rive_common'.    
\> Cannot invoke "String.startsWith(String)" because "versionOutput" is null    
* Try:
\> Run with --stacktrace option to get the stack trace.    
\> Run with --info or --debug option to get more log output.    
\> Run with --scan to get full insights.    
\> Get more help at https://help.gradle.org.    
BUILD FAILED in 4s    
Running Gradle task 'assembleDebug'...                            
6.0s    
Error: Gradle task assembleDebug failed with exit code 1
Even that I didn'tnot add the package of rive.