This compiles fine:

static CatalogNode? findNode(CatalogNode[] rootNodes, Str nodeGuid)
{
  return rootNodes.eachWhile |CatalogNode node|
  {
      findANode(node, nodeGuid)
  }
}

This doesn't (compiler says Cannot return netColarCrmCat::CatalogNode? as sys::Void)

static CatalogNode? findNode(CatalogNode[] rootNodes, Str nodeGuid)
{
  return rootNodes.eachWhile |CatalogNode node|
  {
      echo("hello")
      return findANode(node, nodeGuid)
  }
}

Figure it out

static CatalogNode? findNode(CatalogNode[] rootNodes, Str nodeGuid)
{
  return rootNodes.eachWhile |CatalogNode node -> CatalogNode?|
  {
      echo("hello")
      return findANode(node, nodeGuid)
  }
}

I believe the way closure type inference works today is that all the parameters must have unspecified types if you wish to infer the return type. Not sure that is really the best rule