BUG: Script Crashes processing a simple phrase

[LinuXperia]

Hi.
I tried this phrase here with nai-php but the script crashes with error message.

The Bug and Crash can be reproduced
when using this phrase here instead the one in the example:
$sentence = "I'm extremely happy, I've been";

The Error Crash Message is:

PHP Warning: Array to string conversion in ./NaiPosTagger/src/PosTagging/PosParticiples.php on line 131
PHP Stack trace:
PHP 1. {main}() ./nai-pos-tagger.php:0
PHP 2. NaiPosTagger\Pipelines\PipelinePosTagging->transform($sentence = 'I'm extremely happy, I've been') ./nai-pos-tagger.php:26
PHP 3. NaiPosTagger\Models\NaiDictionary::generateDictionary($sentence = 'ycqzlwprkejivbmndtgsahox I am extremely happy gifkucdmxrjslhwnazyqbvoe i have been ycqzlwprkejivbmndtgsahox') ./NaiPosTagger/src/Pipelines/PipelinePosTagging.php:83
PHP 4. NaiPosTagger\Models\NaiDictionary::posDictionary($pos_arr = [0 => [0 => [...]], 1 => [0 => [...]], 2 => [0 => [...]], 3 => [0 => [...]], 4 => [0 => [...]], 5 => [0 => [...]], 6 => [0 => [...]], 7 => [0 => [...]], 8 => [0 => [...]], 9 => [0 => [...]], 10 => [0 => [...]], 11 => [0 => [...]], 12 => [0 => [...]], 13 => [0 => [...]], 14 => [0 => [...]], 15 => [0 => [...]], 16 => [0 => [...]], 17 => [0 => [...]], 18 => [0 => [...]], 19 => [0 => [...]], 20 => [0 => [...]], 21 => [0 => [...]], 22 => [0 => [...]]]) ./NaiPosTagger/src/Models/NaiDictionary.php:77
PHP 5. NaiPosTagger\Models\NaiPosArr::identifyToken($pos_part = [0 => ['form' => 'been', 'lemma' => '', 'features' => '', 'sh-feat' => '', 'metadata' => [...], 'label' => '', 'rule' => '', 'pos_score' => 0]]) ./NaiPosTagger/src/Models/NaiDictionary.php:133
PHP 6. NaiPosTagger\PosTagging\PosParticiples::transformPartPast($pos_part = [0 => ['form' => 'been', 'lemma' => 'be', 'features' => 'VER:part+past+m+s', 'sh-feat' => 'VER', 'metadata' => [...], 'label' => '', 'rule' => '', 'pos_score' => 0]]) ./NaiPosTagger/src/Models/NaiPosArr.php:153
PHP 7. str_replace($search = '"VER"', $replace = '"ADJ"', $subject = ['ngs' => [305 => [...], 404 => [...]]]) ./NaiPosTagger/src/PosTagging/PosParticiples.php:131
PHP Fatal error: Uncaught TypeError: array_intersect_key(): Argument #1 ($array) must be of type array, string given in ./NaiPosTagger/src/PosTagging/PosNgrams.php:104
Stack trace:
#0 ./NaiPosTagger/src/PosTagging/PosNgrams.php(104): array_intersect_key()
#1 ./NaiPosTagger/src/PosTagging/PosNgrams.php(46): NaiPosTagger\PosTagging\PosNgrams::expandChangingNgrams()
#2 ./NaiPosTagger/src/Pipelines/PipelinePosTagging.php(269): NaiPosTagger\PosTagging\PosNgrams::transform()
#3 ./NaiPosTagger/src/Pipelines/PipelinePosTagging.php(87): NaiPosTagger\Pipelines\PipelinePosTagging->postOperations()
#4 ./nai-pos-tagger.php(26): NaiPosTagger\Pipelines\PipelinePosTagging->transform()
#5 {main}
thrown in ./NaiPosTagger/src/PosTagging/PosNgrams.php on line 104

With other phrase sentences it works but with this specific one it crashes.
What is exactly the problem and how can it be fixed ?
Thanks in advance for any helpful suggestion.