The int() method is used to convert a numeric representation int an integer. It can take a number in any data type such as float, string etc and convert it into an integer number.
You are getting a ValueError as Exception, which means you passed a value that cannot be parsed into an integer value. In your case after looking at the error message it seems that it is because an empty string is being passed as parameter in. To overcome this issue you can wrap your code inside a try except block and skip over invalid entries that might throw an exception. E.G.:
for data in ['', '11', 11.15]:
This code will loop over a list of data and convert it to int if possible and if not then it will catch the exception and won't do anything with it.