Changing PDB document URLs causes an exception

[bartuszekj]

Calling module.Write() after updating PDB document URLs causes a System.ArgumentException.

Code changing the URL is a simple path replacement method:

foreach (var doc in module.PdbState.Documents)
{
    var relPath = Path.GetRelativePath(sourcePath, doc.Url);
    doc.Url = Path.Combine(dstPath, relPath);
}

Exception and stack trace:

System.ArgumentException: An item with the same key has already been added. Key: 30000001
   at System.ThrowHelper.ThrowAddingDuplicateWithKeyArgumentException[T](T key)
   at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior)
   at System.Collections.Generic.Dictionary`2.Add(TKey key, TValue value)
   at dnlib.DotNet.Pdb.PdbState.Add_NoLock(SymbolDocument symDoc)
   at dnlib.DotNet.Pdb.PdbState.AddSequencePoints(CilBody body, SymbolMethod method)
   at dnlib.DotNet.Pdb.PdbState.InitializeMethodBody(ModuleDefMD module, MethodDef ownerMethod, CilBody body)
   at dnlib.DotNet.ModuleDefMD.InitializeBodyFromPdb(MethodDefMD method, CilBody body)
   at dnlib.DotNet.ModuleDefMD.ReadMethodBody(MethodDefMD method, RVA rva, MethodImplAttributes implAttrs, GenericParamContext gpContext)
   at dnlib.DotNet.MethodDefMD.GetMethodBody_NoLock()
   at dnlib.DotNet.MethodDef.InitializeMethodBody()
   at dnlib.DotNet.MethodDef.get_Body()
   at dnlib.DotNet.Writer.Metadata.WriteMethodBodies()
   at dnlib.DotNet.Writer.Metadata.Create()
   at dnlib.DotNet.Writer.Metadata.CreateTables()
   at dnlib.DotNet.Writer.ModuleWriter.WriteImpl()
   at dnlib.DotNet.Writer.ModuleWriterBase.Write(Stream dest)
   at dnlib.DotNet.Writer.ModuleWriterBase.Write(String fileName)
   at dnlib.DotNet.ModuleDef.Write(String filename, ModuleWriterOptions options)

The same exception is thrown when documents are removed via module.PdbState.RemoveAllDocuments() and then readded with new URLs.