Getting NPE error when trying to mock ElasticClient in Mockito I am new to Mockito framework, and I am working on writing tests for the class containing ElasticClient. Below is my actual method: @Service @Slf4j public class CreateIndex {      private final RestHighLevelClient elasticClient;      @Autowired     public IndexService(final RestHighLevelClient elasticClient) throws IOException {         this.elasticClient = elasticClient;     }      public boolean createIndex(String id, String index) {         try {             IndexRequest request = new IndexRequest(index);             request.id(id);             elasticClient.index(request, RequestOptions.DEFAULT);             return true;         } catch (IOException e) {             log.warn(e.getMessage());         }         return false;     }  My test code looks like this: public class TestCreateIndex {    CreateIndex createIndex;     @Mock     RestHighLevelClient elasticClient;     @Rule     public MockitoRule rule = MockitoJUnit.rule();     @Before     public void before() throws IOException {         createIndex = new CreateIndex(elasticClient);     }  @Test     public void TestCreateIndex() throws IOException {             IndexRequest request = new IndexRequest(&quot;1&quot;);             request.id(&quot;1&quot;);             Mockito.when(elasticClient.index(request,(RequestOptions.DEFAULT))).thenReturn(indexResponse);      } }  For the line Mockito.when(elasticClient.index(request,RequestOptions.DEFAULT )).thenReturn(indexResponse);(RequestOptions is some Class), I am getting below error: java.lang.NullPointerException: Cannot invoke &quot;org.elasticsearch.client.RestClient.performRequest(org.elasticsearch.client.Request)&quot; because &quot;this.client&quot; is null      at org.elasticsearch.client.RestHighLevelClient.internalPerformRequest(RestHighLevelClient.java:1514)     at org.elasticsearch.client.RestHighLevelClient.performRequest(RestHighLevelClient.java:1484)     at org.elasticsearch.client.RestHighLevelClient.performRequestAndParseEntity(RestHighLevelClient.java:1454)     at org.elasticsearch.client.RestHighLevelClient.index(RestHighLevelClient.java:871)   Not sure, how to mock elasticClient properly. Please help.
What is a NullPointerException, and how do I fix it? What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?
Solve differential equation, $x'=x^2-2t^{-2}$ Solve differential equation:  $x'=x^2- \frac{2}{t^2}$  Maybe is it sth connected with homogeneous equation? I have no idea how to solve it. Solving ODE with negative expansion power series I am solving a series of ODE, such that each DE is equal to some degree of term that I'm expanding to. For instance, one DE is this:  $\xi^r\partial_r g_{rr}+2g_{tt}\partial_t\xi^t=\mathcal{O}(r)$  $g_{ii}$ are given, from metric, but that's not important. I need to assume that the solution (since I'm looking for components of $\xi^\mu$, which is a vector with components $\xi^t,\xi^r,\xi^\phi$) is given with power series of the form:  $\xi^\mu=\sum\limits_{n}\xi^\mu_n(t,\phi)r^n$, and this is to be seen as expansion around $1/r$ (expansion around $r=\infty$).  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I found tons of links on how to add menu items when doing this: (selecting a folder; )    ...but couldn't find any instructions on how to add menu items when doing this: (not selecting a folder or file)    I did find  and tried adding powershell to HKEY_CLASSES_ROOT\Directory\Background\shell\, (loosely based on the  and linked above) but it didn't work for me.  I'm running Windows 7, by the way.  Also, I'm currently interested in adding only PowerShell, but I'd prefer a general solution I can apply to add any program to the context menu. ssh into an account which has no home directory How to get glare on "Quick Smoke" (Fire & Smoke explosion) How do I install drivers for the RTL8821CE Network Controller on Ubuntu 20.04? My Laptop (HP Laptop 14-ck1xxx) came with the RTL8821CE Network Controller. When I run lspci | grep Network I get: 03:00.0 Network controller: Realtek Semiconductor Co., Ltd. RTL8821CE 802.11ac PCIe Wireless Network Adapter  I‘m unable to get the Wi-Fi to work. 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How can this be solved? "An hour" or "a hour" Dealing with suggested edits on question to be closed as duplicate I would have read this about 20-25 years ago.  I believe the subject was an alien individual, but it could have been a non-standard human instead.  The hook of the story was that the subject lacked an organ like the  that allows the halves of the brain to communicate efficiently, allowing the illusion of a single consciousness.  The subject is conscious, and has thoughts, but is subject to hearing commands like "Wash your hands!" "Fetch water!" within its head.  I recall the subject (and others like the subject) believing that the voices are their gods talking to them.  To the reader it becomes clear that this is a separate part of the subject's own mind that is responsible for long-term planning and simply can't communicate with the rest of the mind in the way a "normal" human is accustomed to. Irreducible polynomial is always separable in char 0 field How to combine complex powers?