Function interp_btreemap_get 

fn interp_btreemap_get(
    args: &[RValue],
    named: &[(String, RValue)],
    context: &BuiltinContext<'_>,
) -> Result<RValue, RError>

Look up a key in a BTreeMap, with an optional default.

@param h integer scalar: btreemap ID @param key character scalar: the key to look up @param default value to return if the key is not found (default NULL) @return the stored value, or default if the key does not exist