fixed release script

Author: fabiocicerchia

Makefile

@@ -218,8 +218,8 @@ benchmark: ## benchmark (wip)
 changelog: ## generate a changelog since previous tag
 	git fetch --all --tags > /dev/null
 	echo "Changes:"
-	git log --pretty=format:"- %B" $(PREVIOUS_TAG)..HEAD | tr '\r' '\n' | grep -Ev '^$$' > CHANGELOG
-	cat CHANGELOG | egrep -v "Automated (metadata|updates)" | sed -e 's/^*/-/' -e 's/"/\\"/g' -e 's/^[ \t]*//' -e 's/^-[ \t]*//' -e 's/^-[ \t]*//' -e 's/^/ - /' | tee CHANGELOG
+	git log --pretty=format:"- %B" $(PREVIOUS_TAG)..HEAD | tr '\r' '\n' | grep -Ev '^$$' || :; > CHANGELOG
+	cat CHANGELOG | egrep -v "Automated (metadata|updates)" | sed -e 's/^*/-/' -e 's/"/\\"/g' -e 's/^[ \t]*//' -e 's/^-[ \t]*//' -e 's/^-[ \t]*//' -e 's/^/ - /' | awk '!x[$$0]++' | tee CHANGELOG
 	echo ""
 	echo "Supported Versions:"
 	cat supported_versions | sed 's/[()"]//g' | tr 'A-Z' 'a-z' | sed 's/^/ - /'