Syntax proposal / pass

Is your feature request related to a problem? Please describe. It is currently needed that every #NODE has a #VARIABLE.

However it can give very ugly cases:

#NODE GP
    #NODE P extends X from "x.gboml"
        #NODE C extends Y from "y.gboml"
            #VARIABLES
        #VARIABLES
    #VARIABLES
    internal: a;

or, worse, without tabulations:

#NODE GP
#NODE P extends X from "x.gboml"
#NODE C extends Y from "y.gboml"
#VARIABLES
#VARIABLES
#VARIABLES
internal: a;

We propose to force users to explicitly "fill" every block with something, to ensure that they understand what is done in the code.

Describe the solution you'd like Introduce a pass keyword, that would be mandatory in empty blocks.

#GLOBAL
    pass;

#NODE x extends a
    pass;

#NODE y extends a
    #VARIABLES
        pass;
    #CONSTRAINTS
        pass;
    #OBJECTIVES
        min v;

#HYPEREDGE e extends e from "e.gboml"
    pass;

//still accepted
#HYPEREDGE e extends e from "e.gboml";
#NODE x extends a;