258     } else if (STAGE_TEXT == root->getType()) {
259         const TextNode* node = static_cast<const TextNode*>(root);
260         IndexDescriptor* desc =
261             collection->getIndexCatalog()->findIndexByKeyPattern(txn, node->indexKeyPattern);
262         invariant(desc);
263         const FTSAccessMethod* fam =
264             static_cast<FTSAccessMethod*>(collection->getIndexCatalog()->getIndex(desc));
265         invariant(fam);
266 
267         TextStageParams params(fam->getSpec());
268         params.index = desc;
269         params.spec = fam->getSpec();
270         params.indexPrefix = node->indexPrefix;
271         // We assume here that node->ftsQuery is an FTSQueryImpl, not an FTSQueryNoop. In practice,
272         // this means that it is illegal to use the StageBuilder on a QuerySolution created by
273         // planning a query that contains "no-op" expressions. TODO: make StageBuilder::build()
274         // fail in this case (this improvement is being tracked by SERVER-21510).
275         params.query = static_cast<FTSQueryImpl&>(*node->ftsQuery);
276         return new TextStage(txn, params, ws, node->filter.get());
277     }