Parameter without default value in a Modelica model

Context: Modelica 3.6 "Undefined modification" feature

In the release announcement of the Modelica language version 3.6 (see Modelica Association Newsletter 2023-01), there is a new syntax Undefined modification:

Undefined modification - this allows making a parameter undefined, e.g., to force users of the model to explicitly set it. https://specification.modelica.org/master/inheritance-modification-and-redeclaration.html#removing-modifiers-break

However, the new syntax, if I understand it correctly, is only to remove the parameter value set the superclass when inheriting a model (with the extends keyword).

Question

Now seeing this new syntax it just occurred to me that I don't know how to specify that a model parameter shouldn't have a default value in general (i.e. force the user of the model to specify its value).

For example, here is a short model where the value of param is not set:

model ParameterDefaultValue "A model with one parameter which shouldn't have a default value"
  parameter Real param "parameter which shouldn't have a default value";
equation

end ParameterDefaultValue;

Even if the value is not specified, this model does simulate, using a default value of 0.0 (in OpenModelica 1.20), albeit with a Translation warning: [ParameterDefaultValue: 2:3-2:73]: Parameter param has no value, and is fixed during initialization (fixed=true), using available start value (start=0.0) as default value.

More specifically, I wonder if it's possible for the simulation to fail rather than emit a warning. In a sense, it means that the model ParameterDefaultValue wouldn't be directly simulable, only after having been extended or simply composed is a larger model:

model UpperModel
  ParameterDefaultValue parameterDefaultValue(param = 1);
equation

end UpperModel;

Relation to partial models

I see that my question resembles the use case of the partial keyword (abstract classes in other object oriented languages), except that partial is:

for underspecified models (not enough equations), not the lack of parameter value
the "partialness" is resolved by extending the model, whereas, as illustrated above, the lack of value can be provided at instantiation (whereas instantiating partial models is forbidden)

Default values in other languages

Also, comparing to an imperative programming languages like Python, the default values of parameters in a function is an optional feature, not a default:

def f(a, b=1):
    return a+b

f(2) # OK → returns 3
f() # fails with TypeError: f() missing 1 required positional argument: 'a'

Solution

I believe that OpenModelica version may be relying on another item that was changed in Modelica 3.6 (due to https://github.com/modelica/ModelicaSpecification/pull/3226 ).

Specifically the messages says it uses the available start-value 0.0, and that seems to refer to the earlier definition of Real that did have a start-value of 0.0 https://specification.modelica.org/maint/3.5/class-predefined-types-and-declarations.html#real-type

Technically the start-value should only be used as default if there was a modifier, but that was a bit unclear and the Pull Request removed the default 0.0 and clarified the use. (There might be additional changes related to this.)

Added: Basically for parameters we can think of three cases:

Nothing, parameter Real p;
Start-default, parameter Real p(start=1);
Value, parameter Real p=1;

The idea is that later ones are "better", but before 3.6 the specification only specified that 2 should give a warning, but didn't really specify anything for 1. I believe that so many relied on the check in Dymola that no-one actually checked whether it was specified.

Note that case 2 was added in 3.3, and updated in https://github.com/modelica/ModelicaSpecification/issues/2136