asDouble method
returns the value at path
as an double.
If the value isn't an double then an exception will be thrown.
If the key isn't a valid int then defaultValue
is returned.
Use validDouble to determine if the key exists and is
a valid double.
Implementation
double asDouble(String path, {double defaultValue = 0.0}) =>
validDouble(path) ? valueMap[path] as double : defaultValue;