Add null guards

src/AzurePolicyEvaluator/AzurePolicyEvaluator.csproj

@@ -12,7 +12,6 @@
 	<PublishReadyToRun>true</PublishReadyToRun>
 	<DebugType>embedded</DebugType>
 	<EnableCompressionInSingleFile>true</EnableCompressionInSingleFile>
-	<RuntimeIdentifier>win-x64</RuntimeIdentifier>
     <InvariantGlobalization>true</InvariantGlobalization>
     <PackageProjectUrl>https://github.com/JanneMattila/azure-policy-evaluator</PackageProjectUrl>
     <RepositoryUrl>https://github.com/JanneMattila/azure-policy-evaluator</RepositoryUrl>

src/AzurePolicyEvaluator/Evaluator.cs

@@ -445,6 +445,8 @@ internal EvaluationResult ExecuteFieldEvaluation(JsonElement fieldObject, JsonEl
                     propertyValue = propertyElement.GetString();
                 }
 
+                ArgumentNullException.ThrowIfNull(propertyValue);
+
                 result = FieldComparison(policy, propertyName, propertyValue);
             }
         }
@@ -528,10 +530,12 @@ internal object RunTemplateFunctions(string text)
                     {
                         throw new KeyNotFoundException($"Parameter {parameters} not found.");
                     }
+                    ArgumentNullException.ThrowIfNull(requiredParameter.DefaultValue);
                     return requiredParameter.DefaultValue;
 
                 case TemplateFunctions.Concat:
                     var concatParameters = parameters as List<string>;
+                    ArgumentNullException.ThrowIfNull(concatParameters);
                     text = string.Join(string.Empty, concatParameters);
                     break;
             }
@@ -613,6 +617,8 @@ internal List<EvaluationResult> ExecuteArrayFieldEvaluation(string propertyName,
                     }
 
                     propertyValue = propertyElement.GetString();
+                    ArgumentNullException.ThrowIfNull(propertyValue);
+
                     var result = FieldComparison(policy, nextName, propertyValue);
                     results.Add(result);
                 }

src/AzurePolicyEvaluator/Program.cs

@@ -3,6 +3,7 @@
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Console;
 using System.CommandLine;
+using System.IO;
 
 IServiceProvider serviceProvider;
 ILogger<Program> logger;
@@ -73,6 +74,8 @@ 1. Evaluate a single policy file against a single test file.
     serviceProvider = services.BuildServiceProvider();
 
     using var loggerFactory = serviceProvider.GetService<ILoggerFactory>();
+    ArgumentNullException.ThrowIfNull(loggerFactory);
+
     logger = loggerFactory.CreateLogger<Program>();
 
     if (watch)
@@ -146,6 +149,8 @@ void PolicyFilesChanged(object sender, FileSystemEventArgs e)
     {
         // Azure Policy file has been changed. Look for test files in sub-folders.
         var policyFolder = Directory.GetParent(policyFilename);
+        ArgumentNullException.ThrowIfNull(policyFolder);
+
         testFiles = Directory.GetFiles(policyFolder.FullName, $"*.{EXTENSION}", SearchOption.AllDirectories)
             .Where(f => Path.GetFileNameWithoutExtension(f) != POLICY_FILE_NAME)
             .ToList();
@@ -155,9 +160,11 @@ void PolicyFilesChanged(object sender, FileSystemEventArgs e)
         // Test file has been changed. Look for policy file in parent folder.
         var testFile = new FileInfo(policyFilename);
         testFiles.Add(testFile.FullName);
-        string policyFile = null;
+        string? policyFile = null;
 
         var directory = testFile.Directory;
+        ArgumentNullException.ThrowIfNull(directory);
+
         while (directory.FullName.Length >= rootFolder.Length)
         {
             logger.LogDebug($"Looking for policy file in {directory.FullName}...");
@@ -168,6 +175,7 @@ void PolicyFilesChanged(object sender, FileSystemEventArgs e)
                 break;
             }
             directory = directory.Parent;
+            ArgumentNullException.ThrowIfNull(directory);
         }
 
         if (policyFile == null)