Trouble with the side transform action Follow

Hello.

I'm trying to reproduce something like VariableDeclaration and its Initializer, that appears when I press the '=' button.

I have one rootable concept Parameter, that implements INamedConcept and has a string property 'value'. Its editor looks like this:

editor for concept Parameter          
  node cell layout:    
    [> {name} ?[> = {value} <] <]

where '=' is a constant cell and the show condition for inner group is

node.value.isNotEmpty

Also it has TransformMenuItem like this:

side transform actions AddInitializer
  right transformed node: Parameter tag: default_ //<no description>
    condition :
      (operationContext, scope, model, sourceNode)->boolean {
        sourceNode.value.isEmpty;
      }
          
    common initializer :
      <no common variables>
      ....................................
      <no common initializer>

    actions :
      add custom items  (output concept: Parameter)
        simple item
          matching text
            =
          description text
            <default>
          icon
            <default>
          type
            <default>
          do transform
            (operationContext, scope, model, sourceNode, pattern)->node<> {
              sourceNode.value.set("zero"); 
              return sourceNode; 
            }

Than I create a new Parameter in the solution, specify some name like 'Param' and press the '=' button. I expect to see something like this:

Param = zero

but nothing happens, the '=' char just added to the parameter name.
What I'm missing?

Thanks,
Alexey