maybeCoatOfArmsPngUrl method
Returns the URL of the PNG image file for the country's coat of arms if it
has one, or null otherwise.
If the hasCoatOfArms property of the WorldCountry object is true,
returns the URL of the PNG image file for the country's coat of arms.
Otherwise, returns null.
Implementation
String? maybeCoatOfArmsPngUrl() =>
hasCoatOfArms ? "$_coatOfArmsProvider/$_lowerCaseCode.$png" : null;