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'use strict';
module.exports = function decorateDiscriminatorIndexOptions(schema, indexOptions) {  // If the model is a discriminator and has an index, add a  // partialFilterExpression by default so the index will only apply  // to that discriminator.  const discriminatorName = schema.discriminatorMapping && schema.discriminatorMapping.value;  if (discriminatorName && !('sparse' in indexOptions)) {    const discriminatorKey = schema.options.discriminatorKey;    indexOptions.partialFilterExpression = indexOptions.partialFilterExpression || {};    indexOptions.partialFilterExpression[discriminatorKey] = discriminatorName;  }  return indexOptions;};