Filtering avoiding unexpected null using lambda's inline

You could do a mapping + filtering before running the forEach part, which also makes it a bit more readable:

disabledUsersOnLDAP.stream()
            .map(user -> usersRepository.findEnabledByUsername(user.getUserName()))
            .filter(userEntity -> userEntity != null)
            .forEach(userEntity -> userEntity.setEnabled(false));

Or as an alternative:

disabledUsersOnLDAP.stream()
            .map(User::getUsername)
            .map(usersRepository::findEnabledByUsername)
            .filter(Objects::nonNull)
            .forEach(userEntity -> userEntity.setEnabled(false));

Some alternatives to the @assylias answser.

Use a method reference to Objects==nonNull for the null check:

disabledUsersOnLDAP.stream()
    .map(User::getUsername)
    .map(usersRepository::findEnabledByUsername)
    .filter(Objects::nonNull)
    .forEach(userEntity -> userEntity.setEnabled(false));

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if you can update UserEntity with a disable method

class UserEntity {
    public void disable() {
        setEnabled(false);
    }
}

you can again use a method reference (UserEntity::disable) :

disabledUsersOnLDAP.stream()
    .map(User::getUsername)
    .map(usersRepository::findEnabledByUsername)
    .filter(Objects::nonNull)
    .forEach(UserEntity::disable);

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Some resources:

• Method References on the java tutorial
• JSR 335: Lambda Expressions for the JavaTM Programming Language