Function Dart_GetError 

pub unsafe extern "C" fn Dart_GetError(
    handle: Dart_Handle,
) -> *const c_char

Gets the error message from an error handle.

Requires there to be a current isolate.

\return A C string containing an error message if the handle is error. An empty C string (“”) if the handle is valid. This C String is scope allocated and is only valid until the next call to Dart_ExitScope.