Fix MonoAOT file name not provided error during benchmark generation. (#2981)

Author: LoopedBard3

src/BenchmarkDotNet/Toolchains/DotNetCli/DotNetCliCommand.cs

@@ -39,7 +39,7 @@ public class DotNetCliCommand
         public DotNetCliCommand(string cliPath, string filePath, string tfm, string? arguments, GenerateResult generateResult, ILogger logger,
             BuildPartition buildPartition, IReadOnlyList<EnvironmentVariable>? environmentVariables, TimeSpan timeout, bool logOutput = false)
         {
-            CliPath = cliPath ?? DotNetCliCommandExecutor.DefaultDotNetCliPath.Value;
+            CliPath = cliPath.IsBlank() ? DotNetCliCommandExecutor.DefaultDotNetCliPath.Value : cliPath;
             Arguments = arguments;
             FilePath = filePath;
             TargetFrameworkMoniker = tfm;

src/BenchmarkDotNet/Toolchains/DotNetCli/DotNetCliCommandExecutor.cs

@@ -106,7 +106,7 @@ internal static ProcessStartInfo BuildStartInfo(string? customDotNetCliPath, str
 
             var startInfo = new ProcessStartInfo
             {
-                FileName = customDotNetCliPath ?? DefaultDotNetCliPath.Value,
+                FileName = customDotNetCliPath.IsBlank() ? DefaultDotNetCliPath.Value : customDotNetCliPath,
                 WorkingDirectory = workingDirectory,
                 Arguments = arguments,
                 UseShellExecute = false,