Do not allow null in observations columns

[petmongrels]

Having null values requires us to check for null instead of using ObservationCollection object. We should keep the values as {} and make it default value. Not making it default may cause the server to break, if null.

Analysis:

• Was created as result of https://github.com/avniproject/data-fixes/issues/2
• The data has become null because of data loss issue - date matches with created_date_time
• If null can be updated on column with default value then not null null constraint also needed
• Also need to check in setting place this check need to be made

[mahalakshme]

@petmongrels this was identified as part of the ticket you worked on yesterday?

the entry that dealt here looks like was created by the IHMP data loss issue(1st time issue)