[processing] Fix merge algorithm

Fix #16292

Author: m-kuhn

python/plugins/processing/algs/qgis/Merge.py

@@ -35,6 +35,7 @@
 from processing.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
 from processing.core.parameters import ParameterMultipleInput
 from processing.core.outputs import OutputVector
+from processing.tools import dataobjects
 
 pluginPath = os.path.split(os.path.split(os.path.dirname(__file__))[0])[0]