could not convert string to float: ''

This error occurs when you try to convert an empty string ('') to a float.

For example:

value = float('')

To fix this error, you need to make sure that the string you are trying to convert to float is not empty. You can check for an empty string using an if statement:

value = ''
if value:
    float_value = float(value)
else:
    float_value = 0.0

This code first checks if the value is not empty using the if statement. If the value is not empty, it is converted to float using the float() function. If the value is empty, the float_value is set to 0.0.