UI - Improved exception dialog shown at early startup failure

Plugins - Provide a better error message on built in plugin installation failure
Conditions - Added better null/not null checks for strings

src/Artemis.Core/DefaultTypes/Conditions/Operators/StringNotNullConditionOperator.cs

@@ -0,0 +1,13 @@
+namespace Artemis.Core
+{
+    internal class StringNotNullConditionOperator : ConditionOperator<string>
+    {
+        public override string Description => "Is not null";
+        public override string Icon => "CheckboxMarkedCircleOutline";
+
+        public override bool Evaluate(string a)
+        {
+            return !string.IsNullOrWhiteSpace(a);
+        }
+    }
+}

src/Artemis.Core/DefaultTypes/Conditions/Operators/StringNullConditionOperator.cs

@@ -0,0 +1,13 @@
+namespace Artemis.Core
+{
+    internal class StringNullConditionOperator : ConditionOperator<string>
+    {
+        public override string Description => "Is null";
+        public override string Icon => "Null";
+
+        public override bool Evaluate(string a)
+        {
+            return string.IsNullOrWhiteSpace(a);
+        }
+    }
+}

src/Artemis.Core/Services/PluginManagementService.cs

@@ -98,11 +98,19 @@ namespace Artemis.Core.Services
                     }
                     else
                     {
+                        PluginInfo pluginInfo;
                         try
                         {
                             // Compare versions, copy if the same when debugging
-                            PluginInfo pluginInfo = CoreJson.DeserializeObject<PluginInfo>(File.ReadAllText(metadataFile))!;
+                            pluginInfo = CoreJson.DeserializeObject<PluginInfo>(File.ReadAllText(metadataFile))!;
+                        }
+                        catch (Exception e)
+                        {
+                            throw new ArtemisPluginException($"Failed read plugin metadata needed to install built-in plugin: {e.Message}", e);
+                        }
 
+                        try
+                        {
                             if (builtInPluginInfo.Version > pluginInfo.Version)
                             {
                                 _logger.Debug("Copying updated built-in plugin from {pluginInfo} to {builtInPluginInfo}", pluginInfo, builtInPluginInfo);
@@ -111,7 +119,7 @@ namespace Artemis.Core.Services
                         }
                         catch (Exception e)
                         {
-                            throw new ArtemisPluginException("Failed read plugin metadata needed to install built-in plugin", e);
+                            throw new ArtemisPluginException($"Failed to install built-in plugin: {e.Message}", e);
                         }
                     }
                 }

src/Artemis.Core/Services/Registration/ConditionOperatorService.cs

@@ -61,6 +61,8 @@ namespace Artemis.Core.Services
             RegisterConditionOperator(Constants.CorePlugin, new StringStartsWithConditionOperator());
             RegisterConditionOperator(Constants.CorePlugin, new StringEndsWithConditionOperator());
             RegisterConditionOperator(Constants.CorePlugin, new StringMatchesRegexConditionOperator());
+            RegisterConditionOperator(Constants.CorePlugin, new StringNullConditionOperator());
+            RegisterConditionOperator(Constants.CorePlugin, new StringNotNullConditionOperator());
 
             // Null checks, at the bottom
             // TODO: Implement a priority mechanism