diff --git a/src/Core/Cache.php b/src/Core/Cache.php
index 7b9f6edd2c..b239af7d60 100644
--- a/src/Core/Cache.php
+++ b/src/Core/Cache.php
@@ -53,7 +53,7 @@ class Cache extends \Friendica\BaseObject
 	 *
 	 * @param string $prefix Prefix of the keys (optional)
 	 *
-	 * @return array|null Null if the driver doesn't support this feature
+	 * @return array Empty if the driver doesn't support this feature
 	 */
 	public static function getAllKeys($prefix = null)
 	{
diff --git a/src/Core/Cache/DatabaseCacheDriver.php b/src/Core/Cache/DatabaseCacheDriver.php
index 9966457467..d90c6e4f18 100644
--- a/src/Core/Cache/DatabaseCacheDriver.php
+++ b/src/Core/Cache/DatabaseCacheDriver.php
@@ -21,18 +21,18 @@ class DatabaseCacheDriver extends AbstractCacheDriver implements ICacheDriver
 		if (empty($prefix)) {
 			$where = ['`expires` >= ?', DateTimeFormat::utcNow()];
 		} else {
-			$where = ['`expires` >= ? AND k LIKE CONCAT(?, \'%\')', DateTimeFormat::utcNow(), $prefix];
+			$where = ['`expires` >= ? AND `k` LIKE CONCAT(?, \'%\')', DateTimeFormat::utcNow(), $prefix];
 		}
 
 		$stmt = DBA::select('cache', ['k'], $where);
 
-		$list = [];
+		$keys = [];
 		while ($key = DBA::fetch($stmt)) {
-			array_push($list, $key['k']);
+			array_push($keys, $key['k']);
 		}
 		DBA::close($stmt);
 
-		return $list;
+		return $keys;
 	}
 
 	/**
diff --git a/src/Core/Cache/ICacheDriver.php b/src/Core/Cache/ICacheDriver.php
index 0a206559cc..2c04c59925 100644
--- a/src/Core/Cache/ICacheDriver.php
+++ b/src/Core/Cache/ICacheDriver.php
@@ -16,7 +16,7 @@ interface ICacheDriver
 	 *
 	 * @param string prefix optional a prefix to search
 	 *
-	 * @return array|null Null if it isn't supported by the cache driver
+	 * @return array Empty if it isn't supported by the cache driver
 	 */
 	public function getAllKeys($prefix = null);
 
diff --git a/src/Core/Cache/MemcachedCacheDriver.php b/src/Core/Cache/MemcachedCacheDriver.php
index 62c3892860..1a6b2a9aef 100644
--- a/src/Core/Cache/MemcachedCacheDriver.php
+++ b/src/Core/Cache/MemcachedCacheDriver.php
@@ -65,7 +65,7 @@ class MemcachedCacheDriver extends AbstractCacheDriver implements IMemoryCacheDr
 			return $this->filterArrayKeysByPrefix($keys, $prefix);
 		} else {
 			logger('Memcached \'getAllKeys\' failed with ' . $this->memcached->getResultMessage(), LOGGER_ALL);
-			return null;
+			return [];
 		}
 	}
 
diff --git a/src/Core/Console/Cache.php b/src/Core/Console/Cache.php
index 459a27e20b..1d93c3c011 100644
--- a/src/Core/Console/Cache.php
+++ b/src/Core/Console/Cache.php
@@ -116,6 +116,7 @@ HELP;
 		$count = 0;
 		foreach ($keys as $key) {
 			$this->out($key);
+			$count++;
 		}
 
 		$this->out($count . ' keys found');