Here my problem:
I get this error:

Uncaught TypeError: Object prototype may only be an Object or null: undefined

export abstract class AbstractLogicExpression {

    protected _logicChildExpressions: AbstractLogicExpression[] = Array();

    protected _precedence = 0;

    protected _parsed = false;

    protected _expressionType = ;



    protected rightAssociative = false;



    public toDNF() {

        for (let i = 0; i < this.logicChildExpressions.length; i++) {

            let actualLogicExpression: AbstractLogicExpression = this.logicChildExpressions[i];



            if (actualLogicExpression._expressionType == ~) {



                let logicConjunction = actualLogicExpression.logicChildExpressions[0];



                let var1 = logicConjunction.logicChildExpressions[0];

                let var2 = logicConjunction.logicChildExpressions[1];



                if (logicConjunction._expressionType == *) {

                    actualLogicExpression.logicChildExpressions[0] = new LogicOr();

                    //actualLogicExpression.logicChildExpressions[0].add(new LogicNeg(var1));

                    //actualLogicExpression.logicChildExpressions[0].add(new LogicNeg(var2));

                }

            }

        }

    }

}

I get this error because of the line before the two commented lines:

actualLogicExpression.logicChildExpressions[0] = new LogicOr();

I tested it by comment and uncomment the lines, because I get no line number in the error message.

Does someone know what I can do?
If you need a little more code. I can post something...

Here the code of LogicOr:
https://pastebin.com/T28Zjbtb