Raise optional warning for missing property keys

[jvita]

It can be challenging to debug issues caused by an incorrectly formatted property_map or missing property keys when uploading data. Currently, adding data will silently "fail" -- no indication is provided that the properties were not actually added.

This is due to the continue statement here. A better alternative may be to change this line to generate an error message that counts how many configurations had missing keys, which is then logged at the end of the loop. This would make it much easier to recognize when there may be something wrong during data upload.