When the parameter of choice type is constant, document generation fails.

[kancve]

Zserio version and language
Zserio: 2.13.0
Language: C++/Doc

Describe the bug
When the parameter of choice type is constant, document generation fails.

How to reproduce
Steps to reproduce the behavior:

• Schema (minimum working example)

package choicetest;

const uint8 COORD_32 = 32;

choice VarCoordXY(uint8 width) on width
{
    case  8: bit:8  coord8;
    case 16: bit:16 coord16;
    case 24: bit:24 coord24;
    case COORD_32: bit:32 coord32;
};

• Zserio command line options

java -jar zserio.jar -src . -cpp cpp -doc doc choicetest.zs

• Error

root@93862d0b4653:/root/schema# java -jar zserio.jar -src . -cpp cpp -doc doc choicetest.zs 
Parsing ./choicetest.zs
Calling C++11 Generator extension check
Calling Doc Generator extension check
Calling Java Generator extension check
Calling Python Generator extension check
Calling XML Generator extension check
Calling C++11 Generator extension
  Generated 3 files
Calling Doc Generator extension
[ERROR] Doc Generator: java.lang.NullPointerException
        at zserio.extension.doc.AstNodeNameMapper.getName(AstNodeNameMapper.java:57)
        at zserio.extension.doc.SymbolTemplateDataCreator.createHtmlTitle(SymbolTemplateDataCreator.java:184)
        at zserio.extension.doc.SymbolTemplateDataCreator.createData(SymbolTemplateDataCreator.java:77)
        at zserio.extension.doc.SymbolTemplateDataCreator.createData(SymbolTemplateDataCreator.java:141)
        at zserio.extension.doc.ChoiceTemplateData$CaseTemplateData.<init>(ChoiceTemplateData.java:95)
        at zserio.extension.doc.ChoiceTemplateData$CaseMemberTemplateData.<init>(ChoiceTemplateData.java:65)
        at zserio.extension.doc.ChoiceTemplateData.<init>(ChoiceTemplateData.java:35)
        at zserio.extension.doc.PackageEmitter.beginChoice(PackageEmitter.java:140)
        at zserio.ast.ZserioAstTreeWalker.visitChoiceType(ZserioAstTreeWalker.java:127)
        at zserio.ast.ChoiceType.accept(ChoiceType.java:48)
        at zserio.ast.Package.visitChildren(Package.java:66)
        at zserio.ast.ZserioAstTreeWalker.visitPackage(ZserioAstTreeWalker.java:42)
        at zserio.ast.Package.accept(Package.java:51)
        at zserio.ast.Root.visitChildren(Root.java:39)
        at zserio.ast.ZserioAstTreeWalker.visitRoot(ZserioAstTreeWalker.java:27)
        at zserio.ast.Root.accept(Root.java:32)
        at zserio.ast.Root.walk(Root.java:66)
        at zserio.extension.doc.DocExtension.process(DocExtension.java:103)
        at zserio.tools.ExtensionManager.process(ExtensionManager.java:122)
        at zserio.tools.ExtensionManager.callExtensions(ExtensionManager.java:87)
        at zserio.tools.ZserioTool.process(ZserioTool.java:163)
        at zserio.tools.ZserioTool.execute(ZserioTool.java:154)
        at zserio.tools.ZserioTool.runTool(ZserioTool.java:83)
        at zserio.tools.ZserioTool.main(ZserioTool.java:66)

root@93862d0b4653:/root/schema#

[Mi-La]

Thanks for the nice and clear report!