Migrate the app to Null Safety

[pawan2806]

Is your feature request related to a problem? Please describe.
With null safety, you can reason about your code with more confidence. No more pesky runtime null dereferencing errors in deployed apps. Instead, you get static errors as you code. ~ dart officials

Describe the solution you'd like
Migrate the app to Null Safety

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

Additional context
Add any other context or screenshots about the feature request here.

#gssoc21_participant

[Samdid]

I would like to work on this issue, also I am a gssoc'21 participant so @pawan2806 please assign it to me

[pawan2806]

I would like to work on this issue, also I am a gssoc'21 participant so @pawan2806 please assign it to me

I am also a participant, waiting for @yashlamba @yashugarg 's response.

[Samdid]

I would like to work on this issue, also I am a gssoc'21 participant so @pawan2806 please assign it to me

I am also a participant, waiting for @yashlamba @yashugarg 's response.

Okay