allow to use null or empty arrays in select->by()

src/Queries/WhereTrait.php

@@ -57,24 +57,32 @@ public function orWhere($where, $marks = null)
     /**
      * Adds a WHERE field = :value clause.
      *
-     * @param string    $field
-     * @param int|array $value
+     * @param string         $field
+     * @param null|int|array $value
      *
      * @return self
      */
     public function by($field, $value)
     {
         if (is_array($value)) {
+            if (empty($value)) {
+                return $this->where("`{$this->entity->name}`.`{$field}` IS NULL");
+            }
+
             return $this->where("`{$this->entity->name}`.`{$field}` IN (:{$field})", [":{$field}" => $value]);
         }
 
+        if ($value === null) {
+            return $this->where("`{$this->entity->name}`.`{$field}` IS NULL");
+        }
+
         return $this->where("`{$this->entity->name}`.`{$field}` = :{$field}", [":{$field}" => $value]);
     }
 
     /**
      * Adds a WHERE id = :id clause.
      *
-     * @param int|array $id
+     * @param null|int|array $id
      *
      * @return self
      */

src/Row.php

@@ -61,7 +61,7 @@ public function __set($name, $value)
     }
 
     /**
-     * Magic method to check if a property is defined or not
+     * Magic method to check if a property is defined or not.
      *
      * @param string $name Property name
      *