MATLAB: How to dispatch optional arguments to nested functions

dispatching argumentsinputparserMATLABoptional arguments

A main function receives a variable number of arguments. It then needs to call other functions that can depend on these optional inputs.
I want to assign a meaningful default value and check the validity of the optional parameter (parameter B in the following example) only in the function that actually uses it (fctB). Unfortunately, I have to assign a value to B in the main function, when I extract it from varargin. At that point the input parser pB considers that parameter B is being passed to fctB and will not use the default value (even though this is what I want).
Here is a code that illustrates the problem:
function dispatch(varargin)
    p = inputParser;
    
    paramName = 'A';
    defaultVal = {};
    addOptional(p,paramName,defaultVal);
    
    paramName = 'B';
    defaultVal = {};
    addOptional(p,paramName,defaultVal);
            
    paramName = 'C';
    defaultVal = {};
    addParameter(p,paramName,defaultVal);
    
    p.parse(varargin{:});
    
    B = p.Results.B;
    
    fctB(B);
end
function fctB(varargin)
    pB = inputParser;
    
    paramName = 'B';
    defaultVal = 10;
    validationFcn = @(x) validateattributes(x,{'numeric'},{'scalar','positive','integer'});
    addOptional(pB,paramName,defaultVal,validationFcn);
    
    pB.parse(varargin{:});
    
    B = pB.Results.B;
    disp(['B = ',num2str(B)]);
end
Calling the function using, for instance, the value B = 2 produces the correct result
dispatch(1,2)
But calling it without arguments will throw an error due to the validation function for B.
Is there a way to pass an argument to a function in such a way that the input parser for that function recognizes that the argument has not been initialized and uses the default value instead? I guess I am looking for something equivalent to the content of an empty cell array {:}.
If this does not exist in MATLAB, how is such a problem resolved in other languages such as C++?

Best Answer

Sumitting my previous comment as an answer to close the question:
[...] As a solution, I have implemented a subclass that overloads some of the methods of the inputParser class. As a result, if the input argument satisfies some criteria, the input parser validation function is bypassed and the default value is assigned.
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