Fix filtering for empty(zero, false) and string values (#99)

* allow to filter by values treated as empty

* fix criteria builder when filtering by string values

Author: jkabat

src/Adapter/Doctrine/ORM/SearchCriteriaProvider.php

@@ -44,7 +44,8 @@ private function processSearchColumns(QueryBuilder $queryBuilder, DataTableState
             $column = $searchInfo['column'];
             $search = $searchInfo['search'];
 
-            if (!empty($search) && null !== ($filter = $column->getFilter())) {
+            if ('' !== trim($search) && null !== ($filter = $column->getFilter())) {
+                $search = $queryBuilder->expr()->literal($search);
                 $queryBuilder->andWhere(new Comparison($column->getField(), $filter->getOperator(), $search));
             }
         }

src/DataTableState.php

@@ -122,7 +122,7 @@ private function handleSearch(ParameterBag $parameters)
             $column = $this->dataTable->getColumn((int) $key);
             $value = $this->isInitial ? $search : $search['search']['value'];
 
-            if ($column->isSearchable() && !empty($value) && null !== $column->getFilter() && $column->getFilter()->isValidValue($value)) {
+            if ($column->isSearchable() && '' !== trim($value) && null !== $column->getFilter() && $column->getFilter()->isValidValue($value)) {
                 $this->setColumnSearch($column, $value);
             }
         }