fix: Handles null values in data during the retrieval

[EXPEbdodla]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

1. Null values are materialized as &types.Value{} instead of nil
2. Added logging when http error occurs
3. Ran go formatting

Other observations #

1. Null values inside arrays are not supported by Materialization
   • INT32, INT64 columns are upcasted to float64 when Null value exists in array. So it fails with invalid type error
   • String arrays fail materialization
   • Materialization works for float, double and timestamp. It's stored as Nan. On Go server side, json encoding not converting NaN to None.
   • Feature server retrieval (GO) doesn't work for float, double
   • Materialization defaults timestamp so its working in Feature server

We need to fix this if necessary