diff --git a/DiscImageChef.Filters/AppleDouble.cs b/DiscImageChef.Filters/AppleDouble.cs
index 258f6f31e..5665a8cec 100644
--- a/DiscImageChef.Filters/AppleDouble.cs
+++ b/DiscImageChef.Filters/AppleDouble.cs
@@ -131,9 +131,11 @@ namespace DiscImageChef.Filters
             string filenameNoExt = Path.GetFileNameWithoutExtension(path);
             string parentFolder  = Path.GetDirectoryName(path);
 
+            parentFolder = parentFolder ?? "";
+            if(filename is null || filenameNoExt is null) return false;
+
             // Prepend data fork name with "R."
-            string ProDosAppleDouble =
-                Path.Combine(parentFolder ?? throw new InvalidOperationException(), "R." + filename);
+            string ProDosAppleDouble = Path.Combine(parentFolder, "R." + filename);
             // Prepend data fork name with '%'
             string UNIXAppleDouble = Path.Combine(parentFolder, "%" + filename);
             // Change file extension to ADF
@@ -141,8 +143,7 @@ namespace DiscImageChef.Filters
             // Change file extension to adf
             string DOSAppleDoubleLower = Path.Combine(parentFolder, filenameNoExt + ".adf");
             // Store AppleDouble header file in ".AppleDouble" folder with same name
-            string NetatalkAppleDouble =
-                Path.Combine(parentFolder, ".AppleDouble", filename ?? throw new InvalidOperationException());
+            string NetatalkAppleDouble = Path.Combine(parentFolder, ".AppleDouble", filename);
             // Store AppleDouble header file in "resource.frk" folder with same name
             string DAVEAppleDouble = Path.Combine(parentFolder, "resource.frk", filename);
             // Prepend data fork name with "._"
@@ -289,9 +290,11 @@ namespace DiscImageChef.Filters
             string filenameNoExt = Path.GetFileNameWithoutExtension(path);
             string parentFolder  = Path.GetDirectoryName(path);
 
+            parentFolder = parentFolder ?? "";
+            if(filename is null || filenameNoExt is null) throw new ArgumentNullException(nameof(path));
+
             // Prepend data fork name with "R."
-            string ProDosAppleDouble =
-                Path.Combine(parentFolder ?? throw new InvalidOperationException(), "R." + filename);
+            string ProDosAppleDouble = Path.Combine(parentFolder, "R." + filename);
             // Prepend data fork name with '%'
             string UNIXAppleDouble = Path.Combine(parentFolder, "%" + filename);
             // Change file extension to ADF
@@ -299,8 +302,7 @@ namespace DiscImageChef.Filters
             // Change file extension to adf
             string DOSAppleDoubleLower = Path.Combine(parentFolder, filenameNoExt + ".adf");
             // Store AppleDouble header file in ".AppleDouble" folder with same name
-            string NetatalkAppleDouble =
-                Path.Combine(parentFolder, ".AppleDouble", filename ?? throw new InvalidOperationException());
+            string NetatalkAppleDouble = Path.Combine(parentFolder, ".AppleDouble", filename);
             // Store AppleDouble header file in "resource.frk" folder with same name
             string DAVEAppleDouble = Path.Combine(parentFolder, "resource.frk", filename);
             // Prepend data fork name with "._"
@@ -543,64 +545,64 @@ namespace DiscImageChef.Filters
         [StructLayout(LayoutKind.Sequential, Pack = 1)]
         struct AppleDoubleHeader
         {
-            public uint magic;
-            public uint version;
+            public readonly uint magic;
+            public readonly uint version;
             [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
-            public byte[] homeFilesystem;
-            public ushort entries;
+            public readonly byte[] homeFilesystem;
+            public readonly ushort entries;
         }
 
         [StructLayout(LayoutKind.Sequential, Pack = 1)]
         struct AppleDoubleEntry
         {
-            public uint id;
-            public uint offset;
-            public uint length;
+            public          uint id;
+            public readonly uint offset;
+            public          uint length;
         }
 
         [StructLayout(LayoutKind.Sequential, Pack = 1)]
         struct AppleDoubleFileDates
         {
-            public uint creationDate;
-            public uint modificationDate;
-            public uint backupDate;
-            public uint accessDate;
+            public readonly uint creationDate;
+            public readonly uint modificationDate;
+            public readonly uint backupDate;
+            public readonly uint accessDate;
         }
 
         [StructLayout(LayoutKind.Sequential, Pack = 1)]
         struct AppleDoubleMacFileInfo
         {
-            public uint creationDate;
-            public uint modificationDate;
-            public uint backupDate;
-            public uint accessDate;
+            public readonly uint creationDate;
+            public readonly uint modificationDate;
+            public readonly uint backupDate;
+            public readonly uint accessDate;
         }
 
         [StructLayout(LayoutKind.Sequential, Pack = 1)]
         struct AppleDoubleUNIXFileInfo
         {
-            public uint creationDate;
-            public uint accessDate;
-            public uint modificationDate;
+            public readonly uint creationDate;
+            public readonly uint accessDate;
+            public readonly uint modificationDate;
         }
 
         [StructLayout(LayoutKind.Sequential, Pack = 1)]
         struct AppleDoubleDOSFileInfo
         {
-            public ushort modificationDate;
-            public ushort modificationTime;
-            public ushort attributes;
+            public readonly ushort modificationDate;
+            public readonly ushort modificationTime;
+            public readonly ushort attributes;
         }
 
         [StructLayout(LayoutKind.Sequential, Pack = 1)]
         struct AppleDoubleProDOSFileInfo
         {
-            public uint   creationDate;
-            public uint   modificationDate;
-            public uint   backupDate;
-            public ushort access;
-            public ushort fileType;
-            public uint   auxType;
+            public readonly uint   creationDate;
+            public readonly uint   modificationDate;
+            public readonly uint   backupDate;
+            public readonly ushort access;
+            public readonly ushort fileType;
+            public readonly uint   auxType;
         }
     }
 }
\ No newline at end of file
diff --git a/DiscImageChef.Filters/PCExchange.cs b/DiscImageChef.Filters/PCExchange.cs
index 44b7a96c1..f06fc5112 100644
--- a/DiscImageChef.Filters/PCExchange.cs
+++ b/DiscImageChef.Filters/PCExchange.cs
@@ -99,8 +99,9 @@ namespace DiscImageChef.Filters
         {
             string parentFolder = Path.GetDirectoryName(path);
 
-            if(!File.Exists(Path.Combine(parentFolder ?? throw new InvalidOperationException(), FINDER_INFO)))
-                return false;
+            parentFolder = parentFolder ?? "";
+
+            if(!File.Exists(Path.Combine(parentFolder, FINDER_INFO))) return false;
 
             if(!Directory.Exists(Path.Combine(parentFolder, RESOURCES))) return false;
 
@@ -164,9 +165,10 @@ namespace DiscImageChef.Filters
             string parentFolder = Path.GetDirectoryName(path);
             string baseFilename = Path.GetFileName(path);
 
+            parentFolder = parentFolder ?? "";
+
             FileStream finderDatStream =
-                new FileStream(Path.Combine(parentFolder ?? throw new InvalidOperationException(), FINDER_INFO),
-                               FileMode.Open, FileAccess.Read);
+                new FileStream(Path.Combine(parentFolder, FINDER_INFO), FileMode.Open, FileAccess.Read);
 
             while(finderDatStream.Position + 0x5C <= finderDatStream.Length)
             {
@@ -223,59 +225,59 @@ namespace DiscImageChef.Filters
             ///     Illegal characters for FAT get substituted with '_' both here and in FAT's LFN entry.
             /// </summary>
             [MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
-            public byte[] macName;
+            public readonly byte[] macName;
             /// <summary>
             ///     File type
             /// </summary>
-            public uint type;
+            public readonly uint type;
             /// <summary>
             ///     File creator
             /// </summary>
-            public uint creator;
+            public readonly uint creator;
             /// <summary>
             ///     Finder flags
             /// </summary>
-            public ushort fdFlags;
+            public readonly ushort fdFlags;
             /// <summary>
             ///     File's icon vertical position within its window
             /// </summary>
-            public ushort verticalPosition;
+            public readonly ushort verticalPosition;
             /// <summary>
             ///     File's icon horizontal position within its window
             /// </summary>
-            public ushort horizontalPosition;
+            public readonly ushort horizontalPosition;
             /// <summary>
             ///     Unknown, all bytes are empty but last, except in volume's label entry
             /// </summary>
             [MarshalAs(UnmanagedType.ByValArray, SizeConst = 18)]
-            public byte[] unknown1;
+            public readonly byte[] unknown1;
             /// <summary>
             ///     File's creation date
             /// </summary>
-            public uint creationDate;
+            public readonly uint creationDate;
             /// <summary>
             ///     File's modification date
             /// </summary>
-            public uint modificationDate;
+            public readonly uint modificationDate;
             /// <summary>
             ///     File's last backup date
             /// </summary>
-            public uint backupDate;
+            public readonly uint backupDate;
             /// <summary>
             ///     Unknown, but is unique, starts 0x7FFFFFFF and counts in reverse.
             ///     Probably file ID for alias look up?
             /// </summary>
-            public uint unknown2;
+            public readonly uint unknown2;
             /// <summary>
             ///     Name as in FAT entry (not LFN).
             ///     Resource fork file is always using this name, never LFN.
             /// </summary>
             [MarshalAs(UnmanagedType.ByValArray, SizeConst = 11)]
-            public byte[] dosName;
+            public readonly byte[] dosName;
             /// <summary>
             ///     Unknown, flags?
             /// </summary>
-            public byte unknown3;
+            public readonly byte unknown3;
         }
     }
 }
\ No newline at end of file