#fixed code
                                public void testMultipleRetrieveCache() {
        String randomApiString = this.getRandomString();

        this.api.saveApi(new ApiResult(0, randomApiString, "privateKey", "", ""));

        for(int i=0; i < 500; i++) {
            Optional<ApiResult> apiByPublicKey = this.api.getApiByPublicKey(randomApiString);

            assertThat(apiByPublicKey.get().getPublicKey()).isEqualTo(randomApiString);
            assertThat(apiByPublicKey.get().getPrivateKey()).isEqualTo("privateKey");
        }

        this.api.deleteApiByPublicKey(randomApiString);
    }
#vulnerable code 
                                public void testMultipleRetrieveCache() {
        String randomApiString = this.getRandomString();

        this.api.saveApi(new ApiResult(0, randomApiString, "privateKey", "", ""));

        for(int i=0; i < 500; i++) {
            ApiResult apiResult = this.api.getApiByPublicKey(randomApiString);

            assertThat(apiResult.getPublicKey()).isEqualTo(randomApiString);
            assertThat(apiResult.getPrivateKey()).isEqualTo("privateKey");
        }

        this.api.deleteApiByPublicKey(randomApiString);
    } 
                            #location 9 
                            #vulnerability type NULL_DEREFERENCE