Account for n/a values in StimulusPresentation

Author: effigies

src/schema/objects/metadata.yaml

@@ -3592,7 +3592,7 @@ ScreenResolution:
     (for example `[1920, 1200]` for a screen of 1920-width by 1080-height pixels),
     if no screen use `n/a`.
     `ScreenResolution` is REQUIRED when the experiment included simultaneous eye-tracking
-    recordings.
+    recordings with `SampleCoordinateSystem` matching `"gaze-on-screen"`.
   anyOf:
     - type: array
       items:
@@ -3610,7 +3610,7 @@ ScreenSize:
     (for example `[0.472, 0.295]` for a screen of 47.2-width by 29.5-height cm),
     if no screen use `n/a`.
     `ScreenSize` is REQUIRED when the experiment included simultaneous eye-tracking
-    recordings.
+    recordings with `SampleCoordinateSystem` matching `"gaze-on-screen"`.
   anyOf:
     - type: array
       items:

src/schema/rules/checks/eyetrack.yaml

@@ -12,10 +12,10 @@ EyetrackingStimulusPresentation:
     - sidecar.PhysioType == 'eyetrack'
     - sidecar.SampleCoordinateSystem == 'gaze-on-screen'
   checks:
-    - '"ScreenDistance" in associations.events.sidecar.StimulusPresentation'
+    - associations.events.sidecar.StimulusPresentation.ScreenDistance != 'n/a'
     - '"ScreenOrigin" in associations.events.sidecar.StimulusPresentation'
-    - '"ScreenResolution" in associations.events.sidecar.StimulusPresentation'
-    - '"ScreenSize" in associations.events.sidecar.StimulusPresentation'
+    - associations.events.sidecar.StimulusPresentation.ScreenResolution != 'n/a'
+    - associations.events.sidecar.StimulusPresentation.ScreenSize != 'n/a'
 
 OnsetSourceConsistency:
   issue: