I cant convert column from string to float (valueerror)

Hey. I need to convert productivity column from str to float(all values in that column is either number or has no value). but the jupyter gives below error:
valueerror: could not convert string to float:

Hey, Elviking.

You need to give a lot more context around this.

Is this part of the content? If it is, what mission and screen is it? Please provide a link.
Is it a guided project? If it is, please share your notebook.
What data is this happening with?
What is the relevant code snippet that yields this error?