code: public Expression getExpectedParam(int index) {
          if (parameters.size() <= index) {
              throw new IllegalArgumentException("Parameter index out of bounds: " + index + ". Function call: " + this);
          }
  
          return parameters.get(index);
      }
docs: Returns the parameter at the expected index.
  
  @param index the number of the parameter to access
  @return the expression representing at the given index
  @throws IllegalArgumentException if the index is out of bounds