Allow specifying empty list for CIDRSliceFlag (#170)

* Allow specifying empty list for CIDRSliceFlag

* Adapt test

* Fix test case name

* Ignore empty value if the flag already contains values

Author: joaopalet

internal/pkg/flags/cidrslice.go

@@ -1,7 +1,6 @@
 package flags
 
 import (
-	"fmt"
 	"strings"
 
 	"github.com/spf13/pflag"
@@ -25,7 +24,12 @@ func (f *cidrSliceFlag) String() string {
 
 func (f *cidrSliceFlag) Set(value string) error {
 	if value == "" {
-		return fmt.Errorf("value cannot be empty")
+		// If it's the first value to be set to the flag, we set it to an empty list
+		// Otherwise, we just ignore an empty value
+		if len(f.value) == 0 {
+			f.value = []string{}
+		}
+		return nil
 	}
 
 	cidrs := strings.Split(value, ",")

internal/pkg/flags/flags_test.go

@@ -586,9 +586,17 @@ func TestCIDRSliceFlag(t *testing.T) {
 			isValid:     false,
 		},
 		{
-			description: "invalid empty value",
-			value1:      utils.Ptr(""),
-			isValid:     false,
+			description:   "empty value to specify empty list",
+			value1:        utils.Ptr(""),
+			isValid:       true,
+			expectedValue: []string{},
+		},
+		{
+			description:   "valid value and empty value",
+			value1:        utils.Ptr("198.51.100.14/24"),
+			value2:        utils.Ptr(""),
+			isValid:       true,
+			expectedValue: []string{"198.51.100.14/24"},
 		},
 		{
 			description: "invalid empty value in list",