Problem with java hibernate

org.springframework.transaction.TransactionSystemException: Could not commit JPA transaction; nested exception is javax.persistence.RollbackException: Error while committing the transaction at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:526) ~[spring-orm-4.3.3.RELEASE.jar!/:4.3.3.RELEASE] at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:761) ~[spring-tx-4.3.3.RELEASE.jar!/:4.3.3.RELEASE] at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:730) ~[spring-tx-4.3.3.RELEASE.jar!/:4.3.3.RELEASE] at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:487) ~[spring-tx-4.3.3.RELEASE.jar!/:4.3.3.RELEASE] at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:291) ~[spring-tx-4.3.3.RELEASE.jar!/:4.3.3.RELEASE] at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96) ~[spring-tx-4.3.3.RELEASE.jar!/:4.3.3.RELEASE] at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.3.RELEASE.jar!/:4.3.3.RELEASE] at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:655) ~[spring-aop-4.3.3.RELEASE.jar!/:4.3.3.RELEASE] at ua.kiev.dobrobutZahyst.services.Services$$EnhancerBySpringCGLIB$$beaa7eb1.addProject(<generated>) ~[classes!/:0.0.1-SNAPSHOT] at ua.kiev.dobrobutZahyst.controllers.AdminController.addProject(AdminController.java:73) ~[classes!/:0.0.1-SNAPSHOT] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_112] at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_112] at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_112] at java.lang.reflect.Method.invoke(Unknown Source) ~[na:1.8.0_112] at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221) ~[spring-web-4.3.3.RELEASE.jar!/:4.3.3.RELEASE] at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136) ~[spring-web-4.3.3.RELEASE.jar!/:4.3.3.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114) ~[spring-webmvc-4.3.3.RELEASE.jar!/:4.3.3.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) ~[spring-webmvc-4.3.3.RELEASE.jar!/:4.3.3.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) ~[spring-webmvc-4.3.3.RELEASE.jar!/:4.3.3.RELEASE] at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) ~[spring-webmvc-4.3.3.RELEASE.jar!/:4.3.3.RELEASE] 

What does this Exception mean? Thank.