Decrypting the Triangle Cipher (Challenge)

# Introduction

In this challenge, we will implement a function called `triangle_decryption` that decrypts characters using a right triangle cipher. The cipher arranges the characters into a right triangle and extracts the hidden message by concatenating the last character of each line. This function will handle cases where characters are not long enough to form a complete triangle and remove leading and trailing spaces. If the input is not a valid string or the empty string, the function returns `None`.