check permission for null values to fix Android build issue in RN 0.77.0-rc.7

[mstrokin]

Summary

Fixes Android build on RN 0.77.0-rc.7

Fixes #921

Test Plan

Update RN to 0.77.0-rc.7 and try to build the project.

• [ X] I have tested this on a device and a simulator
• I added the documentation in README.md
• I added a sample use of the API in the example project (example/App.tsx)

[mikehardy]

root cause - nullability of ReadableArray.getString() changed upstream, first shipped in react-native 0.77, reference facebook/react-native@145c72f#diff-cab6c32d3e05344091c804ea93e8a220dabdd75ec2a258aaf4bde7751c13f844R31

If a simpler patch using the conditional-null operator ?. was used, I think this would work on 0.77 but would fail on 0.76 because kotlin would tell you it could never be null there based on previous typing

using .isNullOrBlank() works around that so I think this should be forwards and backwards compatible

[zoontek]

LGTM, thanks @mstrokin! (and @mikehardy for the explanation)

[zoontek]

Available in 5.2.4