XDCR UI passing in "null" string for empty fields by default

When entering a remote cluster reference, and entering just the SSL information without password as it should, UI is passing a value of "null" to XDCR in the HTML form for those fields that were never touched.

ND: form:

map[certificate:[-----BEGIN CERTIFICATE-----

<redacted>

-----END CERTIFICATE-----] clientCertificate:[null] clientKey:[null] demandEncryption:[true] encryptionType:[full] hostname:[_couchbases._tcp.7cb51b5b-d9cd-410d-9cc7-1be93e2f31d9.dp.cloud.couchbase.com:8091] name:[cloud] password:[null] username:[]]

XDCR parses the HTML form here:
https://github.com/couchbase/goxdcr/blob/8f32b2abcb06a804691090a9227638710935e7cc/replication_manager/msg_utils.go#L304

The correct behavior of all those "null" strings should mirror that of "username", which is empty.

From the reproduced video, it seems that once a text field has text in it, and then removed, then the form is returning the correct "empty" string, which is the correct expectations. However, by default, those fields are returning "null", which is incorrect.