diff --git a/source/StoneAge.Data.FileSystem.Tests/FileSystemTests.cs b/source/StoneAge.Data.FileSystem.Tests/FileSystemTests.cs
index 08f5d4c..77d96a4 100644
--- a/source/StoneAge.Data.FileSystem.Tests/FileSystemTests.cs
+++ b/source/StoneAge.Data.FileSystem.Tests/FileSystemTests.cs
@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.IO;
 using System.Linq;
 using System.Threading.Tasks;
@@ -112,6 +112,25 @@ public async Task WhenFileExist_ExpectItOverWritten()
                 contents.Should().BeEquivalentTo(new byte[5]);
             }
 
+            [Test]
+            public async Task WhenFileDataIsNull_ExpectErrorMessage()
+            {
+                //---------------Arrange-------------------
+                var path = Path.GetTempPath();
+                var fileName = Guid.NewGuid() + ".txt";
+                var document = new DocumentBuilder()
+                                    .With_Name(fileName)
+                                    .With_Bytes(null)    // explicitly set null data
+                                    .Create_Document();
+
+                var sut = new FileSystem();
+                //---------------Act----------------------
+                var result = await sut.Write(path, document);
+                //---------------Assert-----------------------
+                result.HadError.Should().BeTrue();
+                result.ErrorMessages.Should().Contain("No file data provided; cannot write file.");
+            }
+
             private static void Write_File_Contents_For_Testing(string path, string fileName)
             {
                 File.WriteAllText(Path.Combine(path, fileName), "test line");
diff --git a/source/StoneAge.Data.FileSystem/FileSystem.cs b/source/StoneAge.Data.FileSystem/FileSystem.cs
index 008c2ef..ae57b95 100644
--- a/source/StoneAge.Data.FileSystem/FileSystem.cs
+++ b/source/StoneAge.Data.FileSystem/FileSystem.cs
@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
@@ -196,6 +196,13 @@ public async Task<IEnumerable<string>> ReadAllLines(string path)
         private WriteFileResult Write_File_To_Path(IDocument file, string filePath, FileMode fileMode)
         {
             var result = new WriteFileResult();
+
+            if (file.Data == null)
+            {
+                result.ErrorMessages.Add("No file data provided; cannot write file.");
+                return result;
+            }
+
             try
             {
                 using (var stream = new FileStream(filePath, fileMode))