I need help asap

I am making a webbase calcualtor $($using spring mvc$,$ maven on intelliJ$)$

I need help on A only expression because when I run it$,$ it is still asking me to enter something in input B

this is my controller

package com.Junhyeok.webcalculator;

import org.springframework.stereotype.Controller;

import org.springframework.ui$.$Model;

import org.springframework.web.bind.annotation.GetMapping;

import org.springframework.web.bind.annotation.PostMapping;

import org.springframework.web.bind.annotation.RequestParam;

import org.springframework.web.servlet.ModelAndView;

@Controller

public class WebCalculatorController$\{$

$//$ This method handles GET requests to the root URL $("/")$ and displays the calculator form.

@GetMapping$("/")$

public String showCalculator$()\{$

return "calculator";

$\}$

@PostMapping$("/$calculate$")$

public ModelAndView calculate$($

@RequestParam$("$inputA$")$ double inputA,

@RequestParam$($value $=$ "inputB", required $=$ false$)$ Double inputB,

@RequestParam$("$operation$")$ String operation,

Model model$)\{$

double result;

switch $($operation$)\{$

case "add":

result $=$ inputA $+$ inputB;

break;

case "subtract":

result $=$ inputA $-$ inputB;

break;

case "multiply":

result $=$ inputA $*$ inputB;

break;

case "division":

result $=$ inputA $/$ inputB;

break;

case "sin":

result $=$ Math.sin$($inputA$)$;

break;

case "cos":

result $=$ Math.cos$($inputA$)$;

break;

case "tan":

result $=$ Math.tan$($inputA$)$;

break;

case "factorial":

result $=$ factorial$(($int$)$ inputA$)$;

break;

case "power":

result $=$ Math.pow$($inputA$,$ inputB$)$;

break;

case "log":

result $=$ Math.log$($inputA$)/$ Math.log$($inputB$)$;

break;

case "root":

result $=$ Math.pow$($inputA$,1/$ inputB$)$;

break;

case "equal":

result $=$ inputA $==$ inputB $?1$ : $0$;

break;

default:

throw new IllegalArgumentException$("$Invalid operation: $"+$ operation$)$;

$\}$

model.addAttribute$("$result$",$ result$)$;

model.addAttribute$("$inputA$",$ inputA$)$;

if $($inputB $!=$ null$)\{$

model.addAttribute$("$inputB$",$ inputB$)$;

$\}$

model.addAttribute$("$operation$",$ operation$)$;

ModelAndView modelAndView $=$ new ModelAndView$("$calculator$",$ "model", model$)$;

return modelAndView;

$\}$

private double factorial$($double inputA$)\{$

if $($inputA $==0)$

return $1$;

else

return inputA $*$ factorial$($inputA $-1)$;

$\}$

$\}$

and this is my html

Web Calculator

Result: