Make INPUT_EXTRA_REPOS conditional

Only create extra APT sources if any are actually given

This avoids unexpectedly and unnecessarily mixing .list and .sources
files which older APT versions, e.g. in Ubuntu Bionic, did not yet
accept.

Author: funzoneq

scripts/install_build_deps

@@ -24,12 +24,15 @@ fi
 # essential packages. It is reasonably safe to blindly assume it is installed.
 printf "man-db man-db/auto-update boolean false\n" | debconf-set-selections
 
-if printf "%s\n" "$INPUT_EXTRA_REPOS" | grep -q '^deb'; then
-	extra_repos_ext=.list
-else
-	extra_repos_ext=.sources
+if [ -n "$INPUT_EXTRA_REPOS" ]; then
+	if printf "%s\n" "$INPUT_EXTRA_REPOS" | grep -q '^deb'; then
+		extra_repos_ext=.list
+	else
+		extra_repos_ext=.sources
+	fi
+	printf "%s\n" "$INPUT_EXTRA_REPOS" >"/etc/apt/sources.list.d/build-deb-action${extra_repos_ext}"
 fi
-printf "%s\n" "$INPUT_EXTRA_REPOS" >"/etc/apt/sources.list.d/build-deb-action${extra_repos_ext}"
+
 
 apt-get update