Blank WebFlow Form fields are Overwriting Existing Data in Marketo with Blanks

Question

I have reviewed all materials accessible to me, and I cannot figure out why this is occurring. I am capturing UTMs from cookie on my WebFlow site and having them sync to my Marketo via a Marketo form's hidden fields using JavaScript. The JavaScript successfully captures UTMs and passes them to the Marketo form when they exist. The problem is, when they don't exist, it overwrites existing UTM values on the record with blanks. How, if at all, can this be avoided? I am fairly certain that WebFlow is not passing "null", which is what I thought is necessary to overwrite existing data with blank...

Thank you for any help provided.

SanfordWhiteman · Accepted Answer

(Remember to choose the right board. Dynamic Chat is for Marketo’s Dynamic Chat feature, i.e. not for chatting in general!) You are correct that from the client side, only deliberately passing NULL can* empty the field.  When you say “fairly certain“ I’m confused — there can’t be any ambiguity there. Either the form is passing the four-letter string NULL or it isn’t. You can see that in the details of the Filled Out Form activity.  * can, not will, because the update can still be blocked in Admin

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