[processing][grass] Fix skipped outputs are still added in grass commands

python/plugins/processing/algs/grass7/Grass7Algorithm.py

@@ -633,6 +633,7 @@ class Grass7Algorithm(QgsProcessingAlgorithm):
                     uniqueBasename = outName + self.uniqueSuffix
                     command += ' {}={}'.format(outName, uniqueBasename)
                 else:
+                    if outName in parameters and parameters[outName] is not None:
                         # We add an output name to make sure it is unique if the session
                         # uses this algorithm several times.
                         #value = self.parameterAsOutputLayer(parameters, outName, context)