Jamie is a programmer, and James' girlfriend. She likes diamonds, and wants a diamond string from James. Since James doesn't know how to make this happen, he needs your help.
You need to return a string that looks like a diamond shape when printed on the screen, using asterisk (*) characters. Trailing spaces should be removed, and every line must be terminated with a newline character (\n).
Return null/nil/None/... if the input is an even number or negative, as it is not possible to print a diamond of even or negative size.
A size 3 diamond:
*
***
*
...which would appear as a string of " *\n***\n *\n"
A size 5 diamond:
*
***
*****
***
*
...that is: " *\n ***\n*****\n ***\n *\n"