endAngle property
The end of the arc's sweep in radians, measured from the positive x axis. Positive angles turn clockwise.
This will be null if begin and end are horizontally or vertically aligned, or if either is null.
Implementation
double get endAngle {
  if (begin == null || end == null)
    return null;
  if (_dirty)
    _initialize();
  return _beginAngle;
}