Polybius Square Encryption in Python (Challenge)

# Introduction

In this challenge, we will be implementing a function in Python called `polybius_encryption` that takes a string as input and encrypts all the English characters in the string using a 5x5 chessboard. The encryption process involves converting the English letters into two-digit numbers based on their coordinates on the chessboard. The encrypted text should not contain any spaces and should ignore the case of English characters. If the text is empty, the function should return `None`.