fix: ignore empty string env vars when we parse CLI flags (#208)

cmd/lassie/fetch.go

@@ -75,6 +75,11 @@ var fetchCmd = &cli.Command{
 			DefaultText: "Providers will be discovered automatically",
 			Usage:       "Addresses of providers, including peer IDs, to use instead of automatic discovery, seperated by a comma. All protocols will be attempted when connecting to these providers. Example: /ip4/1.2.3.4/tcp/1234/p2p/12D3KooWBSTEYMLSu5FnQjshEVah9LFGEZoQt26eacCEVYfedWA4",
 			Action: func(cctx *cli.Context, v string) error {
+				// Do nothing if given an empty string
+				if v == "" {
+					return nil
+				}
+
 				var err error
 				fetchProviderAddrInfos, err = types.ParseProviderStrings(v)
 				return err

cmd/lassie/flags.go

@@ -97,6 +97,11 @@ var FlagExcludeProviders = &cli.StringFlag{
 	Usage:       "Provider peer IDs, seperated by a comma. Example: 12D3KooWBSTEYMLSu5FnQjshEVah9LFGEZoQt26eacCEVYfedWA4",
 	EnvVars:     []string{"LASSIE_EXCLUDE_PROVIDERS"},
 	Action: func(cctx *cli.Context, v string) error {
+		// Do nothing if given an empty string
+		if v == "" {
+			return nil
+		}
+
 		providerBlockList = make(map[peer.ID]bool)
 		vs := strings.Split(v, ",")
 		for _, v := range vs {
@@ -117,6 +122,11 @@ var FlagProtocols = &cli.StringFlag{
 	Usage:       "List of retrieval protocols to use, seperated by a comma",
 	EnvVars:     []string{"LASSIE_SUPPORTED_PROTOCOLS"},
 	Action: func(cctx *cli.Context, v string) error {
+		// Do nothing if given an empty string
+		if v == "" {
+			return nil
+		}
+
 		var err error
 		protocols, err = types.ParseProtocolsString(v)
 		return err