Updating records with null values (patch)

Thanks for the patch, that does seem to make sense. I'm going to postpone for now, however - I don't have time to extend it to the other entities, and would rather not commit only the node support for 2.3 (thus having the destination plugins behave inconsistently, not to mention the D6 version). After 2.3 is finalized, we can try to complete this for 2.4.

I'm confused as to what the current / desired behaviour is.

What I'm seeing is: Destination fields that are NULL mapped (via addUnmigratedDestinations), end up blank after a migration even when the destination node originally had data. That's definitely not the behaviour that I want ... has a patch for this already gone through?

Ignore my comment, I was confused about the systemOfRecord.

Hi everybody, i am importing my own (self made) site to drupal 7...
I have a node email field (from email module), the problem is when source email field is empty (null), the field is imported with blank value, that caused problem when clicking on the email field (front office) which leads to not found page (404) because the field was imported and it's value is empty.

So what i want to know is : is there a way to import field conditionnaly so that if the source field value is empty the field is not imported at all istead of importing it with empty value ?

Thanks and sorry for my bad english.

PS : I'm new to drupal world ,sorry if my question is a beginer one.
PS: i've also tried the two patchs above which did not solve the problem
========================================================
EDIT:
I've foud a walkaround by unsetting the email field (when source email field is null) in prepare function :-D

I'm having what looks to me like this issue, but with users.

I have a number of text fields on the user entity, added via the field api, saved to features, etc. I'm reading values from the profile tables in Drupal 5.

I have mappings set up for fields, like:

$this->addFieldMapping('field_profile_first_name', 'profile_first_name');
$this->addFieldMapping('field_profile_last_name', 'profile_last_name');

... etc. There are a couple dozen of them. In prepareRow, I add, say, the profile_first_name field to the $row item. At the end of prepareRow, I print_r($row) and only see items I've created. Say, if there was no profile record for a user's first name, then it doesn't show in the dump of $row.

But when the record was created, I still see rows in the field_data_field_profile_first_name table, where the value column is empty.

If I dump $entity in prepare(), it shows this for that first_name field:

[field_profile_first_name] => Array
        (
            [und] => Array
                (
                    [0] => Array
                        (
                            [value_format] => plain_text
                            [format] => plain_text
                            [value] => 
                        )

                )

        )

I'm running the 7.x-2.4-beta1+8-dev of migrate. It's doing this for all text fields. Other fields, such as date fields, link fields, entity_references, etc. don't get the extra records.

@smichel - what you observe is unrelated to this issue, this issue is about updating fields that have values failing to clear those values when they're cleared on the source. If the empty fields are causing you difficulty, please open a separate issue.

Thanks. I realized my issue isn't about updating at all, it's about creating new users. I'll dig into it over the next couple days.