Looking at your stack trace it seems that your Compta
class is not in any package. This can cause problems (see http://docs.spring.io/spring-boot/docs/current/reference//htmlsingle/#using-boot-using-the-default-package) so I'd try putting all of your classes in a package first.
Also check that your AccountRepository
is in the same package, or a sub-package of Compta
.
If you're still having problems, perhaps you can share a complete project that replicates the problem?