code: public static void assertParameterNotNull(CodeBuilder b, int paramIndex) {
          b.loadLocal(b.getParameter(paramIndex));
          Label notNull = b.createLabel();
          b.ifNullBranch(notNull, false);
          throwException(b, IllegalArgumentException.class, null);
          notNull.setLocation();
      }
docs: Generate code to throw an exception if a parameter is null
  @param b CodeBuilder into which to append the code
  @param paramIndex index of the parameter to check