Addresses Peer-Review
Addresses Peer-Review

`first_valid_index´ has been removed for now as it doesn't have a satifactory init test. It will be added in a future commit.

StefanoRaggi/Lean,StefanoRaggi/Lean,AlexCatarino/Lean,jameschch/Lean,JKarathiya/Lean,QuantConnect/Lean,JKarathiya/Lean,jameschch/Lean,AlexCatarino/Lean,jameschch/Lean,StefanoRaggi/Lean,QuantConnect/Lean,StefanoRaggi/Lean,AlexCatarino/Lean,jameschch/Lean,jameschch/Lean,QuantConnect/Lean,QuantConnect/Lean,StefanoRaggi/Lean,JKarathiya/Lean,JKarathiya/Lean,AlexCatarino/Lean