code: private void genNullCheck(DiagnosticPosition pos) {
          if (allowBetterNullChecks) {
              callMethod(pos, syms.objectsType, names.requireNonNull,
                      List.of(syms.objectType), true);
          } else {
              callMethod(pos, syms.objectType, names.getClass,
                      List.nil(), false);
          }
          code.emitop0(pop);
      }
docs: Generate a null check from the object value at stack top.