Update view extension apply method

- allow for optional arguments in apply
- raise error if all arguments are None

Author: tyler-c2s

pystac/extensions/view.py

@@ -28,11 +28,11 @@ def __init__(self, item):
         self.item = item
 
     def apply(self,
-              off_nadir=None,
-              incidence_angle=None,
-              azimuth=None,
-              sun_azimuth=None,
-              sun_elevation=None):
+              off_nadir: Optional[float] = None,
+              incidence_angle: Optional[float] = None,
+              azimuth: Optional[float] = None,
+              sun_azimuth: Optional[float] = None,
+              sun_elevation: Optional[float] = None):
         """Applies View Geometry extension properties to the extended Item.
 
         Args:
@@ -49,11 +49,21 @@ def apply(self,
             sun_elevation (float): Sun elevation angle. The angle from the tangent of the scene
                 center point to the sun. Measured from the horizon in degrees (0-90).
         """
-        self.off_nadir = off_nadir
-        self.incidence_angle = incidence_angle
-        self.azimuth = azimuth
-        self.sun_azimuth = sun_azimuth
-        self.sun_elevation = sun_elevation
+        if (off_nadir is None and incidence_angle is None and azimuth is None
+                and sun_azimuth is None and sun_elevation is None):
+            raise pystac.STACError(
+                'Must provide at least one of: off_nadir, incidence_angle, azimuth, sun_azimuth, sun_elevation'  # noqa: E501
+            )
+        if off_nadir:
+            self.off_nadir = off_nadir
+        if incidence_angle:
+            self.incidence_angle = incidence_angle
+        if azimuth:
+            self.azimuth = azimuth
+        if sun_azimuth:
+            self.sun_azimuth = sun_azimuth
+        if sun_elevation:
+            self.sun_elevation = sun_elevation
 
     @property
     def off_nadir(self):