### Question:
ApiClient { public ApiClient setHttpClient(OkHttpClient newHttpClient) { this.httpClient = Objects.requireNonNull(newHttpClient, "HttpClient must not be null!"); return this; } ApiClient();  ApiClient(OkHttpClient client);  ApiClient(String clientId);  ApiClient(String clientId, Map<String, String> parameters);  ApiClient(String clientId, String clientSecret, Map<String, String> parameters);  ApiClient(String basePath, String clientId, String clientSecret, Map<String, String> parameters); String getBasePath(); ApiClient setBasePath(String basePath); OkHttpClient getHttpClient(); ApiClient setHttpClient(OkHttpClient newHttpClient); JSON getJSON(); ApiClient setJSON(JSON json); boolean isVerifyingSsl(); ApiClient setVerifyingSsl(boolean verifyingSsl); InputStream getSslCaCert(); ApiClient setSslCaCert(InputStream sslCaCert); KeyManager[] getKeyManagers(); ApiClient setKeyManagers(KeyManager[] managers); DateFormat getDateFormat(); ApiClient setDateFormat(DateFormat dateFormat); ApiClient setSqlDateFormat(DateFormat dateFormat); ApiClient setOffsetDateTimeFormat(DateTimeFormatter dateFormat); ApiClient setLocalDateFormat(DateTimeFormatter dateFormat); ApiClient setLenientOnJson(boolean lenientOnJson); Map<String, Authentication> getAuthentications(); Authentication getAuthentication(String authName); void setUsername(String username); void setPassword(String password); void setApiKey(String apiKey); void setApiKeyPrefix(String apiKeyPrefix); void setAccessToken(String accessToken); ApiClient setUserAgent(String userAgent); ApiClient addDefaultHeader(String key, String value); ApiClient addDefaultCookie(String key, String value); boolean isDebugging(); ApiClient setDebugging(boolean debugging); String getTempFolderPath(); ApiClient setTempFolderPath(String tempFolderPath); int getConnectTimeout(); ApiClient setConnectTimeout(int connectionTimeout); int getReadTimeout(); ApiClient setReadTimeout(int readTimeout); int getWriteTimeout(); ApiClient setWriteTimeout(int writeTimeout); TokenRequestBuilder getTokenEndPoint(); String parameterToString(Object param); List<Pair> parameterToPair(String name, Object value); List<Pair> parameterToPairs(String collectionFormat, String name, Collection value); String collectionPathParameterToString(String collectionFormat, Collection value); String sanitizeFilename(String filename); boolean isJsonMime(String mime); String selectHeaderAccept(String[] accepts); String selectHeaderContentType(String[] contentTypes); String escapeString(String str); @SuppressWarnings("unchecked") T deserialize(Response response, Type returnType); RequestBody serialize(Object obj, String contentType); File downloadFileFromResponse(Response response); File prepareDownloadFile(Response response); ApiResponse<T> execute(Call call); ApiResponse<T> execute(Call call, Type returnType); void executeAsync(Call call, ApiCallback<T> callback); @SuppressWarnings("unchecked") void executeAsync(Call call, final Type returnType, final ApiCallback<T> callback); T handleResponse(Response response, Type returnType); Call buildCall(String path, String method, List<Pair> queryParams, List<Pair> collectionQueryParams, Object body, Map<String, String> headerParams, Map<String, String> cookieParams, Map<String, Object> formParams, String[] authNames, ApiCallback callback); Request buildRequest(String path, String method, List<Pair> queryParams, List<Pair> collectionQueryParams, Object body, Map<String, String> headerParams, Map<String, String> cookieParams, Map<String, Object> formParams, String[] authNames, ApiCallback callback); String buildUrl(String path, List<Pair> queryParams, List<Pair> collectionQueryParams); void processHeaderParams(Map<String, String> headerParams, Request.Builder reqBuilder); void processCookieParams(Map<String, String> cookieParams, Request.Builder reqBuilder); void updateParamsForAuth(String[] authNames, List<Pair> queryParams, Map<String, String> headerParams, Map<String, String> cookieParams); RequestBody buildRequestBodyFormEncoding(Map<String, Object> formParams); RequestBody buildRequestBodyMultipart(Map<String, Object> formParams); String guessContentTypeFromFile(File file);  }### Answer:
@Test(expected = NullPointerException.class) public void testNullHttpClient() { apiClient.setHttpClient(null); }