Fix various small warnings

[MGaetan89]

This commit addresses the following warnings:

• Remove unnecessary semi-colons.
• Use isEmpty() instead of comparing the size to 0 (for collections) or the value to "" (for strings).
• Remove unnecessary calls to toString().
• Remove redundant type declarations.
• Use Kotlin's property instead of getter/setter.
• Replace redundant StringBuilder with String.
• Remove unnecessary casts.

[rohitjoins]

I'm going to send this for internal review now. You may see some more commits being added as I make changes in response to review feedback. Please refrain from pushing any more substantive changes as it will complicate the internal review - thanks!