convenient implementation TryFrom<&Option<String>> for MacAddress (#983)

## Problem

When we parse xml, the address field is optional and we use
`Option<String>` as type. For this it is convenient to have such a
TryFrom implementation as well.

## Testing

- *Added a new unit test*

rust/agama-dbus-server/src/network/model.rs

@@ -161,6 +161,57 @@ mod tests {
  use crate::network::error::NetworkStateError;
  use uuid::Uuid;
 
+ #[test]
+ fn test_macaddress() {
+ let mut val: Option<String> = None;
+ assert!(matches!(
+ MacAddress::try_from(&val).unwrap(),
+ MacAddress::Unset
+ ));
+
+ val = Some(String::from(""));
+ assert!(matches!(
+ MacAddress::try_from(&val).unwrap(),
+ MacAddress::Unset
+ ));
+
+ val = Some(String::from("preserve"));
+ assert!(matches!(
+ MacAddress::try_from(&val).unwrap(),
+ MacAddress::Preserve
+ ));
+
+ val = Some(String::from("permanent"));
+ assert!(matches!(
+ MacAddress::try_from(&val).unwrap(),
+ MacAddress::Permanent
+ ));
+
+ val = Some(String::from("random"));
+ assert!(matches!(
+ MacAddress::try_from(&val).unwrap(),
+ MacAddress::Random
+ ));
+
+ val = Some(String::from("stable"));
+ assert!(matches!(
+ MacAddress::try_from(&val).unwrap(),
+ MacAddress::Stable
+ ));
+
+ val = Some(String::from("This is not a MACAddr"));
+ assert!(matches!(
+ MacAddress::try_from(&val),
+ Err(InvalidMacAddress(_))
+ ));
+
+ val = Some(String::from("de:ad:be:ef:2b:ad"));
+ assert_eq!(
+ MacAddress::try_from(&val).unwrap().to_string(),
+ String::from("de:ad:be:ef:2b:ad").to_uppercase()
+ );
+ }
+
  #[test]
  fn test_add_connection() {
  let mut state = NetworkState::default();
@@ -457,6 +508,17 @@ impl FromStr for MacAddress {
  }
 }
 
+impl TryFrom<&Option<String>> for MacAddress {
+ type Error = InvalidMacAddress;
+
+ fn try_from(value: &Option<String>) -> Result<Self, Self::Error> {
+ match &value {
+ Some(str) => MacAddress::from_str(str),
+ None => Ok(Self::Unset),
+ }
+ }
+}
+
 impl fmt::Display for MacAddress {
  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  let output = match &self {