docs: function negationSelector(selectorContext) {
      // If no properties currently selected, select them all first.
      if (isEmpty(selectorContext.sourceKeys)) {
          extendSourceKeys(selectorContext.sourceKeys, selectorContext.source);
      }
      // Then remove the negated property.
      if (selectorContext.sourceKeys[selectorContext.sourceKey] !== undefined) {
          delete selectorContext.sourceKeys[selectorContext.sourceKey];
  
      } else {
          // Throw error if negated property not found.
          errorManager.propertyNotFound(selectorContext.sourceKey, selectorContext.source);
      }
  }