fix(#246): login email on blur validation (#57)

src/features/Login/hooks.tsx

@@ -18,7 +18,8 @@ export const useLoginForm = () => {
   const { login } = useAuthStore()
 
   const onEmailBlur = ({ target }: FocusEvent<HTMLInputElement>) => {
-    if (!isValidEmail(target.value)) {
+    const email = target.value
+    if (email && !isValidEmail(email)) {
       updateFormError(formIds.email, 'error_invalid_email_format')
     }
   }