Can not compile empty namespace

[benkinooby]

Hi,

I want to compile the ModelDesign of an empty namespace but it fails with

PS C:\UA-ModelCompiler\Bin\Release> .\Opc.Ua.ModelCompiler.exe -d2 C:\opcua-modeling-tutorial\FooFltModel.xml -cg C:\opcua-modeling-tutorial\FooFltModel.csv -o C:\opcua-modeling-tutorial\FooFltModel -console
Object reference not set to an instance of an object.
   at Opc.Ua.ModelCompiler.ModelCompilerValidator.Validate2(IList`1 designFilePaths, String identifierFilePath, Boolean generateIds) in C:\UA-ModelCompiler\ModelCompiler\ModelDesignerValidator.cs:line 1099
   at Opc.Ua.ModelCompiler.ModelGenerator2.ValidateAndUpdateIds(IList`1 designFilePaths, String identifierFilePath, UInt32 startId, String specificationVersion) in C:\UA-ModelCompiler\ModelCompiler\ModelGenerator2.cs:line 95
   at Opc.Ua.ModelCompiler.Program.ProcessCommandLine2(List`1 tokens) in C:\UA-ModelCompiler\ModelCompiler\Program.cs:line 422

Here is the ModelDesign file I am trying to compile.

<?xml version="1.0" encoding="utf-8"?>

<ModelDesign
  xmlns:uax="http://opcfoundation.org/UA/2008/02/Types.xsd"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:ua="http://opcfoundation.org/UA/"
  xmlns:FooZbrFlt="https://new.foo.com/zebra-compression/flattening-and-subspacefolding/UA/"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema"
  TargetNamespace="https://new.foo.com/zebra-compression/flattening-and-subspacefolding/UA/"
  TargetVersion="0.9.0"
  TargetPublicationDate="2020-05-01T00:00:00Z"
  xmlns="http://opcfoundation.org/UA/ModelDesign.xsd">

  <Namespaces>
    <!--No space allowed at the beginning of the namespace URL!
      Prefix sets the filenames of the generated files. -->
    <Namespace Name="FooZbrFlt" Prefix="FooFlt">https://new.foo.com/zebra-compression/flattening-and-subspacefolding/UA/</Namespace>
    <Namespace Name="OpcUa" Version="1.03" PublicationDate="2013-12-02T00:00:00Z">http://opcfoundation.org/UA/</Namespace>
  </Namespaces>
    
  <!-- Instantiate at least one variable (or object, or view, or ...) in namespace.
    Compiling an empty namespace will fail with error message:
	Object reference not set to an instance of an object.
    Uncomment to following view and the ModelDesign will compile successfully. -->
  
  <!-- 
  <View SymbolicName="FooZbrFlt:MyView">
    <Description>Dummy view.</Description>
    <References>
      <Reference IsInverse="true">
        <ReferenceType>ua:Organizes</ReferenceType>
        <TargetId>ua:ObjectsFolder</TargetId>
      </Reference>
    </References>
  </View>
  -->
</ModelDesign>

The model design file will compile successfully, if the view is uncommented and the namespace therefore is not empty.

Is this a bug of UA-ModelCompiler?

[opcfoundation-org]

Not sure it is a priority. An empty file serves no purpose.

[benkinooby]

Certainly not a priority but it has a purpose:

It allows you to test your server and toolchain without any knowledge about Nodesets and models. It's an edge case, but a rather helpful one. It helps you to start from scratch with your model/nodeset, which is a reasonable first step when starting with OPC UA modelling and getting to know variables, types, etc.

It has a workaround (adding e.g. a view as shown above) too, lowering the priority even further. But it is a confusing bug that will mainly be hit by newcomers.

[opcfoundation-org]

Fixed in NET 5.0 version.