import math


def degrees(rad_angle) :
    """Converts any angle in radians to degrees.

    If the input is None, the it returns None.
    For numerical input, the output is mapped to [-180,180]
    """
    if rad_angle is None :
        return None
    angle = rad_angle * 180 / math.pi
    while angle > 180 :
        angle = angle - 360
    while angle < -180 :
        angle = angle + 360
    return angle