fix: handle nullable filter edge cases for empty and not-null values

src/Filters/FiltersOperator.php

@@ -39,6 +39,12 @@ public function __invoke(Builder $query, $value, string $property)
         } elseif ($this->filterOperator->isDynamic() && $value !== null) {
             $filterOperator = $this->getDynamicFilterOperator($value);
             $this->removeDynamicFilterOperatorFromValue($value, $filterOperator);
+        } elseif ($this->filterOperator->isDynamic() && $value === null) {
+            $filterOperator = FilterOperator::EQUAL;
+        }
+
+        if ($value === '') {
+            $value = null;
         }
 
         $query->where($query->qualifyColumn($property), $filterOperator->value, $value, $this->boolean);

tests/FilterTest.php

@@ -934,6 +934,35 @@ public function __invoke(Builder $query, $value, string $property): Builder
     expect($results->first()->name)->toBeNull();
 });
 
+it('can filter with dynamic operator filter when value is empty string', function () {
+    TestModel::create(['name' => null, 'salary' => 1000]);
+    TestModel::create(['name' => 'John', 'salary' => 2000]);
+
+    $results = createQueryFromFilterRequest([
+        'name' => '',
+    ])
+        ->allowedFilters(AllowedFilter::operator('name', FilterOperator::DYNAMIC)->nullable())
+        ->get();
+
+    expect($results)->toHaveCount(1);
+    expect($results->first()->name)->toBeNull();
+});
+
+it('can filter with not-equal dynamic operator filter when value is empty after operator', function () {
+    TestModel::create(['name' => null, 'salary' => 1000]);
+    TestModel::create(['name' => 'John', 'salary' => 2000]);
+
+    $results = createQueryFromFilterRequest([
+        'name' => '<>',
+    ])
+        ->allowedFilters(AllowedFilter::operator('name', FilterOperator::DYNAMIC)->nullable())
+        ->get();
+
+    // Empty value after <> produces IS NOT NULL: null-name model excluded, named model included
+    expect($results->pluck('name')->contains(null))->toBeFalse();
+    expect($results->where('salary', 2000)->first()?->name)->toBe('John');
+});
+
 it('throws RelationNotFoundException when the relation method exists but does not return an Eloquent Relation', function () {
     $ModelWithNonRelationMethod = new class () extends TestModel {
         protected $table = 'test_models';