diff --git a/src/Database/Query/Select.php b/src/Database/Query/Select.php
index 4eb53a0..32b409c 100644
--- a/src/Database/Query/Select.php
+++ b/src/Database/Query/Select.php
@@ -97,28 +97,28 @@ class Select
         return $this;
     }
 
-    public function where($column, string $relation = null, $value = null): Select
+    public function where($column, ?string $relation = null, $value = null): Select
     {
         $this->addWhereCondition('AND', $column, $relation, $value);
 
         return $this;
     }
 
-    public function orWhere($column, string $relation = null, $value = null): Select
+    public function orWhere($column, ?string $relation = null, $value = null): Select
     {
         $this->addWhereCondition('OR', $column, $relation, $value);
 
         return $this;
     }
 
-    public function having($column, string $relation = null, $value = null): Select
+    public function having($column, ?string $relation = null, $value = null): Select
     {
         $this->addHavingCondition('AND', $column, $relation, $value);
 
         return $this;
     }
 
-    public function orHaving($column, string $relation = null, $value = null): Select
+    public function orHaving($column, ?string $relation = null, $value = null): Select
     {
         $this->addHavingCondition('OR', $column, $relation, $value);
 
@@ -211,12 +211,12 @@ class Select
         $this->joins[] = [$type, $table, $column1, $relation, $column2];
     }
 
-    private function addWhereCondition(string $logic, $column, string $relation, $value): void
+    private function addWhereCondition(string $logic, $column, ?string $relation, $value): void
     {
         $this->conditions[self::CONDITION_WHERE][] = [$logic, $column, $relation, $value];
     }
 
-    private function addHavingCondition(string $logic, $column, string $relation, $value): void
+    private function addHavingCondition(string $logic, $column, ?string $relation, $value): void
     {
         $this->conditions[self::CONDITION_HAVING][] = [$logic, $column, $relation, $value];
     }