diff --git a/src/NuGetMirror/FileLogger.cs b/src/NuGetMirror/FileLogger.cs
index 863ecab..6aedb9b 100644
--- a/src/NuGetMirror/FileLogger.cs
+++ b/src/NuGetMirror/FileLogger.cs
@@ -6,17 +6,11 @@ namespace NuGetMirror
 {
     public class FileLogger : LoggerBase
     {
-        private static readonly object _lockObj = new object();
+        private static readonly object _lockObj = new();
 
         public bool Enabled { get; set; } = true;
-
         public ILogger OutputLogger { get; }
-
         public string OutputPath { get; }
-
-        /// <summary>
-        /// Verbosity to filter on for the file.
-        /// </summary>
         public LogLevel FileLoggerVerbosity { get; set; } = LogLevel.Error;
 
         public FileLogger(ILogger output, string outputPath)
@@ -27,6 +21,9 @@ public FileLogger(ILogger output, string outputPath)
         public FileLogger(ILogger output, LogLevel level, string outputPath)
             : base(LogLevel.Debug)
         {
+            ArgumentNullException.ThrowIfNull(output);
+            ArgumentException.ThrowIfNullOrWhiteSpace(outputPath);
+
             FileLoggerVerbosity = level;
             OutputLogger = output;
             OutputPath = outputPath;
@@ -34,17 +31,17 @@ public FileLogger(ILogger output, LogLevel level, string outputPath)
 
         public override void Log(ILogMessage message)
         {
-            // Always pass the message to the inner logger.
+            ArgumentNullException.ThrowIfNull(message);
+
             OutputLogger.Log(message);
 
-            if ((int)message.Level >= (int)FileLoggerVerbosity)
+            if (message.Level >= FileLoggerVerbosity)
             {
                 lock (_lockObj)
                 {
-                    using (var writer = new StreamWriter(File.Open(OutputPath, FileMode.Append, FileAccess.Write)))
-                    {
-                        writer.WriteLine(message);
-                    }
+                    using var writer = new StreamWriter(
+                        File.Open(OutputPath, FileMode.Append, FileAccess.Write));
+                    writer.WriteLine(message.Message);
                 }
             }
         }
@@ -52,8 +49,7 @@ public override void Log(ILogMessage message)
         public override Task LogAsync(ILogMessage message)
         {
             Log(message);
-
-            return Task.FromResult(0);
+            return Task.CompletedTask;
         }
     }
 }