"?" instead of type parameter value for Linq functions

[YImhof]

Using the option outputFormatting in H5 configuration file, transpilled JS code can be directly minified.
This worked great with Bridge.Net and also with H5, but now I have a project whose H5 compilation raises the following exception:
[fail] [10:20:27] Error minifiying code. Saved output to [/path/to/tmp/file]
System.NullReferenceException: Object reference not set to an instance of an object.

H5 is actually using NUglify 1.20.7 for this operation. So using a minimal project, I tried to find the line(s) causing the NUglify exception(s), feeding it with H5's temp output.

What I found is that for an unknown reason, when I am using System.Linq functions, H5 define the type variable with a type named "?" instead of the real type name, like "Element" for example. When I manually change the "?" for the correct type name, then NUglify correctly proceeds the code ... until the next misnamed type parameter.

This problem does not occur in a systematic way, as for example in my minimal project, which is a copy-paste of several classes of the original project, type parameters are correctly transpilled. I have to admit that this project's H5 formatted result (so its beautified javascript output) is about 3.7 [Mb] (~ 32'000 lines length), which is why I'm using the minified option. I tried for example to use intermediate IEnumerable<Element> variables in C# code, but H5 keeps using "?" as type parameter value

Is there any size limit for H5 compiler? Am I doing something wrong? Any other idea?

Example illustrating transpilation error

Original C# code example (rootContainer is a H5.Core.dom.HTMLDivElement and is inherited) :

namespace ANamespace
{
    public class AClassName : AParentClassName
    {
        public int Index
        {
            get
            {
                if (rootContainer.parentNode != null)
                    return rootContainer.parentElement.children.ToList().IndexOf(rootContainer);
                else
                    return -1;
            }
        }
    }
}

Javascript transpilation result of the H5 compiler (from temp saved output):
Notice the return ($t = ?, in the beginning of the line 8.

H5.define("ANamespace.AClassName", {
    inherits: [AParentClassName],
    props: {
        Index: {
            get: function () {
                var $t;
                /*##|24,186,17|##*/if (/*##|24,186,21|##*/this.rootContainer.parentNode != /*##|24,186,49|##*/null) {
                    /*##|24,187,21|##*/return /*##|24,187,28|##*/($t = /*##|24,187,58|##*/?, System.Linq.Enumerable.from(/*##|24,187,79|##*/this.rootContainer.parentElement.children, $t).toList($t)).indexOf(/*##|24,187,125|##*/this.rootContainer);
                } else {
                    /*##|24,189,21|##*/return /*##|24,189,28|##*/-1;
                }
            }
        }
    }
});