[FEATURE] Nullable event attributes

[sandeep-ps]

Is your feature request related to a problem? Please describe.
Currently, according to the API spec, Event attributes are not nullable. That means an empty string must be added to Event attributes, which creates additional overhead when writing code.

Describe the solution you'd like
If event attributes can be marked nullable in the Events API specification, clients can send event JSON objects with null values for optional fields.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
In the source code, optional attributes should be checked for null values if they are not being done currently.