Correct behavior of flatMap method - #52

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

* [Useless overriding method] Possible useless method overriding detected

* [Useless overriding method] Possible useless method overriding detected

* [Useless overriding method] Possible useless method overriding detected

* [Useless overriding method] Possible useless method overriding detected

* [Useless overriding method] Possible useless method overriding detected

* [Useless overriding method] Possible useless method overriding detected

* [Line length] Line exceeds 80 characters; contains 90 characters * [Space after not] Expected 1 space after NOT operator; 0 found

* [Return type hint] Method \PetrKnap\Optional\JavaSe8\OptionalTestCase::dataMatchesJavaBehavior() does not have @return annotation for its traversable return value. * [Function length] Your function is too long. Currently using 23 lines. Can be up to 20 lines.

* [Array indent] Closing brace of array declaration must be on a new line

* [Eval] Use of eval() is discouraged