diff --git a/FFMpegCore.Test/ArgumentBuilderTest.cs b/FFMpegCore.Test/ArgumentBuilderTest.cs
index 687c76e..08be2f8 100644
--- a/FFMpegCore.Test/ArgumentBuilderTest.cs
+++ b/FFMpegCore.Test/ArgumentBuilderTest.cs
@@ -9,10 +9,10 @@ namespace FFMpegCore.Test
     [TestClass]
     public class ArgumentBuilderTest : BaseTest
     {
-        List<string> concatFiles = new List<string>
+        private List<string> concatFiles = new List<string>
         { "1.mp4", "2.mp4", "3.mp4", "4.mp4"};
 
-        FFArgumentBuilder builder;
+        private FFArgumentBuilder builder;
 
         public ArgumentBuilderTest() : base()
         {
@@ -21,7 +21,7 @@ public ArgumentBuilderTest() : base()
 
         private string GetArgumentsString(params Argument[] args)
         {
-            var container = new ArgumentContainer {new InputArgument("input.mp4")};
+            var container = new ArgumentContainer { new InputArgument("input.mp4") };
             foreach (var a in args)
             {
                 container.Add(a);
@@ -31,7 +31,6 @@ private string GetArgumentsString(params Argument[] args)
             return builder.BuildArguments(container);
         }
 
-
         [TestMethod]
         public void Builder_BuildString_IO_1()
         {
@@ -80,8 +79,7 @@ public void Builder_BuildString_BitStream()
         [TestMethod]
         public void Builder_BuildString_Concat()
         {
-            var container = new ArgumentContainer {new ConcatArgument(concatFiles), new OutputArgument("output.mp4")};
-
+            var container = new ArgumentContainer { new ConcatArgument(concatFiles), new OutputArgument("output.mp4") };
 
             var str = builder.BuildArguments(container);
 
@@ -96,7 +94,6 @@ public void Builder_BuildString_Copy_Audio()
             Assert.AreEqual(str, "-i \"input.mp4\" -c:a copy \"output.mp4\"");
         }
 
-
         [TestMethod]
         public void Builder_BuildString_Copy_Video()
         {
@@ -188,7 +185,7 @@ public void Builder_BuildString_Speed()
         [TestMethod]
         public void Builder_BuildString_DrawtextFilter()
         {
-            var str = GetArgumentsString(new DrawTextArgument("Stack Overflow", "/path/to/font.ttf", 
+            var str = GetArgumentsString(new DrawTextArgument("Stack Overflow", "/path/to/font.ttf",
                 ("fontcolor", "white"),
                 ("fontsize", "24"),
                 ("box", "1"),
@@ -212,7 +209,7 @@ public void Builder_BuildString_StartNumber()
         public void Builder_BuildString_Threads_1()
         {
             var str = GetArgumentsString(new ThreadsArgument(50));
-            
+
             Assert.AreEqual(str, "-i \"input.mp4\" -threads 50 \"output.mp4\"");
         }
 
@@ -224,7 +221,6 @@ public void Builder_BuildString_Threads_2()
             Assert.AreEqual(str, $"-i \"input.mp4\" -threads {Environment.ProcessorCount} \"output.mp4\"");
         }
 
-
         [TestMethod]
         public void Builder_BuildString_Codec()
         {
@@ -242,10 +238,21 @@ public void Builder_BuildString_Codec_Override()
         }
 
         [TestMethod]
-        public void Builder_BuildString_Duration() {
+        public void Builder_BuildString_Duration()
+        {
             var str = GetArgumentsString(new DurationArgument(TimeSpan.FromSeconds(20)));
 
             Assert.AreEqual(str, "-i \"input.mp4\" -t 00:00:20 \"output.mp4\"");
         }
+
+        [TestMethod]
+        public void Builder_BuildString_Raw()
+        {
+            var str = GetArgumentsString(new CustomArgument(null));
+            Assert.AreEqual(str, "-i \"input.mp4\"  \"output.mp4\"");
+
+            str = GetArgumentsString(new CustomArgument("-acodec copy"));
+            Assert.AreEqual(str, "-i \"input.mp4\" -acodec copy \"output.mp4\"");
+        }
     }
-}
+}
\ No newline at end of file
diff --git a/FFMpegCore/FFMPEG/Argument/Atoms/CustomArgument.cs b/FFMpegCore/FFMPEG/Argument/Atoms/CustomArgument.cs
new file mode 100644
index 0000000..6a38b4e
--- /dev/null
+++ b/FFMpegCore/FFMPEG/Argument/Atoms/CustomArgument.cs
@@ -0,0 +1,14 @@
+namespace FFMpegCore.FFMPEG.Argument
+{
+    public class CustomArgument : Argument<string>
+    {
+        public CustomArgument(string argument) : base(argument)
+        {
+        }
+
+        public override string GetStringValue()
+        {
+            return Value ?? string.Empty;
+        }
+    }
+}
\ No newline at end of file