Replace an object in the list or leave the same one using Stream.map()

There is a list of elements. Task: if a record is found in the database by the name of the field of an element from the list, create a new object from the found record and insert it instead of the existing element. If not, leave the element in the list (do nothing).

Sample code:

result = list.stream().map(element -> {
    Optional<Object> dbRecord = repository.findByName(element.getName());

    dbRecord.ifPresent(
            x -> {
                x.setSmth(element.getSmth());
                x.setSmth1(element.getSmth1());
                ...
            }
    );

    return dbRecord.orElse(element);

}).collect(Collectors.toList());

I've checked in the debugger - at any steps method repository.findByName() returns Optional.enpty(). The second call to return with the returning of element, I catch an error:

org.springframework.dao.IncorrectResultSizeDataAccessException: query did not return a unique result: 2; nested exception is javax.persistence.NonUniqueResultException: query did not return a unique result: 2
    at org.springframework.orm.jpa.EntityManagerFactoryUtils.convertJpaAccessExceptionIfPossible(EntityManagerFactoryUtils.java:385) ~[spring-orm-5.3.14.jar:5.3.14]
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:235) ~[spring-orm-5.3.14.jar:5.3.14]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:551) ~[spring-orm-5.3.14.jar:5.3.14]
    at org.springframework.dao.support.ChainedPersistenceExceptionTranslator.translateExceptionIfPossible(ChainedPersistenceExceptionTranslator.java:61) ~[spring-tx-5.3.14.jar:5.3.14]
    at org.springframework.dao.support.DataAccessUtils.translateIfNecessary(DataAccessUtils.java:242) ~[spring-tx-5.3.14.jar:5.3.14]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:152) ~[spring-tx-5.3.14.jar:5.3.14]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.14.jar:5.3.14]
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:145) ~[spring-data-jpa-2.6.0.jar:2.6.0]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.14.jar:5.3.14]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:97) ~[spring-aop-5.3.14.jar:5.3.14]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.14.jar:5.3.14]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:215) ~[spring-aop-5.3.14.jar:5.3.14]
    at com.sun.proxy.$Proxy186.findByName(Unknown Source) ~[?:?]
    at ru.app.MyService.lambda$processRequest$4(MyService.java:166) ~[my-application-2.0.0.jar:?]

I understand how to solve the problem with a general loop, but I would like to understand how the stream.map() method works. Tell me please, what is my mistake?