Fix number comparisons for position values

src/measurements/MeasurementBuilder.js

@@ -40,7 +40,7 @@ class MeasurementBuilder {
     if (!this.variant) {
       throw new Error('Measurement variant is required');
     }
-    if (!this.position) {
+    if (Number.isNaN(this.position)) {
       throw new Error('Measurement position is required');
     }
 

src/measurements/MeasurementContainer.js

@@ -284,7 +284,7 @@ class MeasurementContainer {
 
   // Helper methods
   _ensureChainIsValid() {
-    if (!this._currentType || !this._currentVariant || !this._currentPosition) {
+    if (!this._currentType || !this._currentVariant || Number.isNaN(this._currentPosition)) {
       if (this.logger) {
         this.logger.error('Incomplete measurement chain, required: type, variant, and position');
       }