Function string_val_parser_opt 

pub fn string_val_parser_opt(
    data: &mut HashMap<String, Option<String>>,
    key: &'static str,
) -> Result<Option<String>, Ts3Error>

Helper function to retrieve optional string value from line-hashmap, (re)moves value.

use ts3_query::*;
use std::collections::HashMap;

let mut v: HashMap<String, Option<String>> =
    vec![("abc".to_string(), Some("asd".to_string())),
    ("def".to_string(), None)]
    .into_iter().collect();
assert_eq!(Some("asd".to_string()),raw::string_val_parser_opt(&mut v, "abc").unwrap());
assert_eq!(None,raw::string_val_parser_opt(&mut v, "def").unwrap());