[Harness] If empty nodes are found, do not crash. (#8201)

Looks like we have cases in which we get empty nodes when listing
devices, which makes the parsing of the nodes fail and crash.

Move the code to a diff method, try to parse the data, if there is an
exception (missing data) return null. If null is returned, do not add
it.

Fixes: https://github.com/xamarin/xamarin-macios/issues/8160

tests/xharness/Hardware/Devices.cs

@@ -58,6 +58,33 @@ namespace Xharness.Hardware {
 			return LoadAsync (log, extra_data: false, removed_locked: !include_locked, force: force);
 		}
 
+		Device GetDevice (XmlNode deviceNone)
+		{
+			// get data, if we are missing some of them, we will return null, happens sometimes that we 
+			// have some empty nodes. We could do this with try/catch, but we want to throw the min amount
+			// of exceptions. We do know that we will have issues with the parsing of the DeviceClass, check
+			// the value, and if is there, get the rest, else return null
+			var usable = deviceNone.SelectSingleNode ("IsUsableForDebugging")?.InnerText;
+			if (Enum.TryParse<DeviceClass> (deviceNone.SelectSingleNode ("DeviceClass")?.InnerText, true, out var deviceClass)) { 
+				var device = new Device {
+					DeviceIdentifier = deviceNone.SelectSingleNode ("DeviceIdentifier")?.InnerText,
+					DeviceClass = deviceClass,
+					CompanionIdentifier = deviceNone.SelectSingleNode ("CompanionIdentifier")?.InnerText,
+					Name = deviceNone.SelectSingleNode ("Name")?.InnerText,
+					BuildVersion = deviceNone.SelectSingleNode ("BuildVersion")?.InnerText,
+					ProductVersion = deviceNone.SelectSingleNode ("ProductVersion")?.InnerText,
+					ProductType = deviceNone.SelectSingleNode ("ProductType")?.InnerText,
+					InterfaceType = deviceNone.SelectSingleNode ("InterfaceType")?.InnerText,
+					IsUsableForDebugging = usable == null ? (bool?) null : ((bool?) (usable == "True")),
+				};
+				bool.TryParse (deviceNone.SelectSingleNode ("IsLocked")?.InnerText, out var locked);
+				device.IsLocked = locked;
+				return device;
+			} else {
+				return null;
+			}
+		}
+
 		public async Task LoadAsync (ILog log, bool extra_data = false, bool removed_locked = false, bool force = false)
 		{
 			if (loaded) {
@@ -94,20 +121,9 @@ namespace Xharness.Hardware {
 						doc.LoadWithoutNetworkAccess (tmpfile);
 
 						foreach (XmlNode dev in doc.SelectNodes ("/MTouch/Device")) {
-							var usable = dev.SelectSingleNode ("IsUsableForDebugging")?.InnerText;
-							Device d = new Device {
-								DeviceIdentifier = dev.SelectSingleNode ("DeviceIdentifier")?.InnerText,
-								DeviceClass = (DeviceClass) Enum.Parse(typeof(DeviceClass), dev.SelectSingleNode ("DeviceClass")?.InnerText, true),
-								CompanionIdentifier = dev.SelectSingleNode ("CompanionIdentifier")?.InnerText,
-								Name = dev.SelectSingleNode ("Name")?.InnerText,
-								BuildVersion = dev.SelectSingleNode ("BuildVersion")?.InnerText,
-								ProductVersion = dev.SelectSingleNode ("ProductVersion")?.InnerText,
-								ProductType = dev.SelectSingleNode ("ProductType")?.InnerText,
-								InterfaceType = dev.SelectSingleNode ("InterfaceType")?.InnerText,
-								IsUsableForDebugging = usable == null ? (bool?)null : ((bool?)(usable == "True")),
-							};
-							bool.TryParse (dev.SelectSingleNode ("IsLocked")?.InnerText, out var locked);
-							d.IsLocked = locked;
+							var d = GetDevice (dev);
+							if (d == null)
+								continue;
 							if (removed_locked && d.IsLocked) {
 								log.WriteLine ($"Skipping device {d.Name} ({d.DeviceIdentifier}) because it's locked.");
 								continue;

tests/xharness/Xharness.Tests/Samples/devices.xml

@@ -1,6 +1,40 @@
 <?xml version="1.0" encoding="utf-8"?>
 <MTouch Version="0" Revision="0">
   <SdkRoot>/Applications/Xcode113.app/Contents/Developer</SdkRoot>
+  <Device>
+    <ActivationState />
+    <AmountDataAvailable />
+    <BatteryCurrentCapacity />
+    <BluetoothAddress />
+    <BuildVersion />
+    <ChipID />
+    <CPUArchitecture />
+    <DeveloperStatus />
+    <DeviceClass />
+    <DeviceColor />
+    <DeviceEnclosureColor />
+    <DeviceIdentifier>5696DC36EE3249859D465DA37E6EA912</DeviceIdentifier>
+    <DevToolsAvailable />
+    <EnableWifiDebugging />
+    <HardwareModel />
+    <InterfaceType>Wifi</InterfaceType>
+    <InternationalMobileEquipmentIdentity />
+    <IsPaired>False</IsPaired>
+    <IsUsableForDebugging />
+    <IsValid>True</IsValid>
+    <ModelNumber />
+    <Name>Office</Name>
+    <PasswordProtected />
+    <ProductionSOC />
+    <ProductType />
+    <ProductVersion />
+    <SerialNumber />
+    <TotalDataCapacity />
+    <UDID />
+    <UniqueChipID />
+    <WatchCompanionCapability />
+    <WiFiAddress />
+  </Device>
   <Device>
     <ActivationState>Activated</ActivationState>
     <AmountDataAvailable>5650776064</AmountDataAvailable>