Update getRelatedIndexes.js

Author: vkarpov15

lib/helpers/indexes/getRelatedIndexes.js

@@ -1,5 +1,7 @@
 'use strict';
 
+const hasDollarKeys = require('../query/hasDollarKeys');
+
 function getRelatedSchemaIndexes(model, schemaIndexes) {
   return getRelatedIndexes({
     baseModelName: model.baseModelName,
@@ -48,7 +50,7 @@ function getRelatedIndexes({
     const partialFilterExpression = getPartialFilterExpression(index, indexesType);
     return !partialFilterExpression
       || !partialFilterExpression[discriminatorKey]
-      || partialFilterExpression[discriminatorKey]['$exists'];
+      || (hasDollarKeys(partialFilterExpression[discriminatorKey]) && !('$eq' in partialFilterExpression[discriminatorKey]));
   });
 }