code: public Instruction createList(final Instruction _newTail) {
        Instruction childExprHead = null;
        if (_newTail == null) {
           childExprHead = head;
           tail = head = null;
        } else {
           childExprHead = _newTail.getNextExpr();
           tail = _newTail;
           _newTail.setNextExpr(null);
           if (childExprHead != null) {
              childExprHead.setPrevExpr(null);
           }
  
        }
        return (childExprHead);
     }
docs: [1] [2] [3] [4]
  
  Note that passing null here essentially deletes the existing expression list and returns the expression
  
  @param _newTail
  @return