Extracting characters between double quotes

In my project I need to extract some parameters from a settings file. Below is a section of the line that I am reading, the parameter I need to extract is the Program Prefix.

...  ProgramPrefix="" ReceiveTimeout="80000" ...

I need to extract what is between the double quotes for ProgramPrefix. The problem is that in-between these quotes can be any alphanumeric character, symbol, space, or no character at all.

Below is my current solution for extracting any character before the second double-quote, the problem it doesn't work for the case of nothing being between the double quotes

    EOPdefL = string.find(line,"ProgramPostfix=")
    EOPdef = string.match(line,'([^"]+)',EOPdefL+16)

When there is nothing in-between the double quotes the output for EOPdef is:

EOPdef = ReceiveTimeout=

I would like EOPdef to just return an empty string if there are no characters.

EOPdef = ""