Drop unique constraint on 'cif' in debitures table

Remove the unique constraint on the 'cif' field in the debitures table and refactor the `UniqueCifExceptZero` validation rule to handle the uniqueness check more robustly. Also, add an unused import statement for `UniqueExcept` in `DebitureRequest`.

app/Http/Requests/DebitureRequest.php

@@ -4,6 +4,7 @@
 
     use Illuminate\Foundation\Http\FormRequest;
     use Modules\Lpj\Rules\UniqueCifExceptZero;
+    use Modules\Lpj\Rules\UniqueExcept;
 
     class DebitureRequest extends FormRequest
     {

app/Rules/UniqueCifExceptZero.php

@@ -1,25 +1,32 @@
 <?php
 
-namespace Modules\Lpj\Rules;
+    namespace Modules\Lpj\Rules;
 
-use Closure;
-use Illuminate\Contracts\Validation\ValidationRule;
-use Modules\Lpj\Models\Debiture;
+    use Closure;
+    use Illuminate\Contracts\Validation\ValidationRule;
+    use Modules\Lpj\Models\Debiture;
 
-class UniqueCifExceptZero implements ValidationRule
-{
-    public function __construct($id = null)
+    class UniqueCifExceptZero implements ValidationRule
     {
-        $this->id = $id;
-    }
+        protected $id;
 
-    public function validate($attribute, $value, $fail): void
-    {
-        if (Debiture::where($attribute, $value)
-                 ->where('id', '!=', $this->id)
-                 ->where($attribute, '!=', '0000000000')
-                 ->exists()) {
-            $fail('The :attribute field must be uniquse.'.$this->id);
+        public function __construct($id = null)
+        {
+            $this->id = $id;
+        }
+
+        /**
+         * Run the validation rule.
+         */
+        public function validate(string $attribute, mixed $value, Closure $fail)
+        : void {
+            if ($value !== '0000000000' && $value !== null && Debiture::query()->where($attribute, $value)->when(
+                        $this->id,
+                        function ($query) {
+                            $query->where('id', '!=', $this->id);
+                        },
+                    )->exists()) {
+                $fail('The :attribute field must be unique.');
+            }
         }
     }
-}