[BUGFIX][Processing][Rscript] Write to R_OUTPUT_VALUES file if saveOutputValues

Fixes #16618 Processing rscripts: cannot concatenate 'str' and 'NoneType' objects

Author: rldhont

python/plugins/processing/algs/r/RAlgorithm.py

@@ -413,7 +413,7 @@ def getExportCommands(self):
                 value = out.value
                 value = value.replace('\\', '/')
                 commands.append('write.csv(' + out.name + ',"' + value + '")')
-            elif out.name != RAlgorithm.R_OUTPUT_VALUES:
+            elif out.name != RAlgorithm.R_OUTPUT_VALUES and self.saveOutputValues:
                 commands.append('cat("##' + out.name + '",file="' + outputDataFile + '",sep="\n",append=TRUE)')
                 commands.append('cat(' + out.name + ',file="' + outputDataFile + '",sep="\n",append=TRUE)')