Removed unnecessary null check in cpaitalizeFirst and capitalize method

[sumitsharansatsangi]

• Removing unneessary check results in null-exempt string .i. e. earlier return type was String? now it becomes String *

Every PR must update the corresponding documentation in the code, and also the readme in english with the following changes.

Pre-launch Checklist

• [] I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making or feature I am adding, or @jonataslaw said the PR is test-exempt.
• All existing and new tests are passing.

[jonataslaw]

LGTM

[jonataslaw]

Thank you for your contribution!