title: Spring declarative caching and null values handling
body: <p>I have set up Spring declarative caching but I am not sure how to handle null values and I am seeking advice and best practices in order to properly use my cache.</p>
  
  <p>I have the following Spring Data Repository method that returns <strong><code>null</code></strong> if no <code>Member</code> is found given the email passed in argument:</p>
  
  <pre><code>@Cacheable(value = "database-cache")
  Member findByEmail(String email);
  </code></pre>
  
  <p>Of course, the null value returned will cause a <code>NullPointerException</code> as follows:</p>
  
  <pre><code>GRAVE: Servlet.service() for servlet [bignibou] in context with path [/bignibou] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
  java.lang.NullPointerException
      at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:191)
      at com.google.common.cache.LocalCache.put(LocalCache.java:4210)
      at org.springframework.cache.concurrent.ConcurrentMapCache.put(ConcurrentMapCache.java:121)
      at org.springframework.cache.interceptor.CacheAspectSupport$CachePutRequest.apply(CacheAspectSupport.java:459)
      at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:226)
      at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:181)
      at org.springframework.cache.interceptor.CacheInterceptor.invoke(CacheInterceptor.java:60)
      at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
      at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207)
      at com.sun.proxy.$Proxy80.findByEmail(Unknown Source)
      at com.bignibou.service.preference.PreferenceServiceImpl.isEmailAvailable_aroundBody0(PreferenceServiceImpl.java:42)
      at com.bignibou.service.preference.PreferenceServiceImpl$AjcClosure1.run(PreferenceServiceImpl.java:1)
      at org.springframework.transaction.aspectj.AbstractTransactionAspect.ajc$around$org_springframework_transaction_aspectj_AbstractTransactionAspect$1$2a73e96cproceed(AbstractTransactionAspect.aj:59)
      at org.springframework.transaction.aspectj.AbstractTransactionAspect$AbstractTransactionAspect$1.proceedWithInvocation(AbstractTransactionAspect.aj:65)
      at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:262)
      at org.springframework.transaction.aspectj.AbstractTransactionAspect.ajc$around$org_springframework_transaction_aspectj_AbstractTransactionAspect$1$2a73e96c(AbstractTransactionAspect.aj:63)
      at com.bignibou.service.preference.PreferenceServiceImpl.isEmailAvailable(PreferenceServiceImpl.java:40)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:483)
      at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317)
      at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:201)
      at com.sun.proxy.$Proxy99.isEmailAvailable(Unknown Source)
      at com.bignibou.controller.preference.PreferenceController.sendPasswordResetInformation(PreferenceController.java:113)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:483)
      at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
      at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
      at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
      at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:749)
      at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:689)
      at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
      at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
      at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
      at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
      at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
      at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
      at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
      at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:118)
      at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:84)
      at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
      at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:113)
      at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
      at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:103)
      at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
      at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:113)
      at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
      at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:154)
      at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
      at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:45)
      at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
      at org.springframework.security.web.authentication.www.BasicAuthenticationFilter.doFilter(BasicAuthenticationFilter.java:150)
      at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
      at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:199)
      at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
      at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:110)
      at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
      at org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:105)
      at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
      at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
      at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:57)
      at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
      at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
      at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:87)
      at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
      at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:50)
      at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
      at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
      at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:192)
      at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:160)
      at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:344)
      at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:261)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
      at org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter.doFilterInternal(OpenEntityManagerInViewFilter.java:177)
      at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
      at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
      at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
      at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
      at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
      at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
      at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
      at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
      at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
      at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
      at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
      at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
      at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
      at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
      at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
      at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
      at java.lang.Thread.run(Thread.java:745)
  </code></pre>
  
  <p>Should I just:</p>
  
  <ul>
  <li>configure my <code>ConcurrentMapCache</code> to allow null values (set <code>allowNullValues</code> to true) and call it a day? </li>
  <li>am I missing something and is there a better way of proceeding?</li>
  </ul>
  
  <p>Any comment and advice welcome.</p>