Selection::getPreviousAccessedColumns must return array [Closes #160]

Author: hranicka

src/Database/Table/Selection.php

@@ -156,9 +156,9 @@ public function getSql(): string
 	/**
 	 * Loads cache of previous accessed columns and returns it.
 	 * @internal
-	 * @return array|bool
+	 * @return array
 	 */
-	public function getPreviousAccessedColumns()
+	public function getPreviousAccessedColumns(): array
 	{
 		if ($this->cache && $this->previousAccessedColumns === NULL) {
 			$this->accessedColumns = $this->previousAccessedColumns = $this->cache->load($this->getGeneralCacheKey());