Add null check for logger before logging errors in position validation

src/measurements/MeasurementContainer.js

@@ -427,7 +427,9 @@ class MeasurementContainer {
         return Number.NEGATIVE_INFINITY;
       
       default:
+        if (this.logger) {
           this.logger.error(`Invalid positionVsParent provided: ${positionString}`);
+        }
         return;
     }
   }
@@ -442,8 +444,10 @@ class MeasurementContainer {
     if (positionValue > 0) {
       return "downstream";
     }
+    if (this.logger) {
       this.logger.error(`Invalid position provided: ${positionValue}`);
     }
+  }
 
 }