diff --git a/src/server/session.ts b/src/server/session.ts
index 86d87ad023fda..dc5cc9a9628ec 100644
--- a/src/server/session.ts
+++ b/src/server/session.ts
@@ -412,6 +412,7 @@ namespace ts.server {
                 let progress = false;
                 perProjectResults.forEach((referencedSymbols, project) => {
                     if (updatedProjects.has(project)) return;
+                    if (!referencedSymbols) return;
                     const updated = project.getLanguageService().updateIsDefinitionOfReferencedSymbols(referencedSymbols, knownSymbolSpans);
                     if (updated) {
                         updatedProjects.add(project);
@@ -423,6 +424,7 @@ namespace ts.server {
 
             perProjectResults.forEach((referencedSymbols, project) => {
                 if (updatedProjects.has(project)) return;
+                if (!referencedSymbols) return;
                 for (const referencedSymbol of referencedSymbols) {
                     for (const ref of referencedSymbol.references) {
                         ref.isDefinition = false;
@@ -441,27 +443,29 @@ namespace ts.server {
         // Otherwise, it just ends up attached to the first corresponding def we happen to process.  The others may or may not be
         // dropped later when we check for defs with ref-count 0.
         perProjectResults.forEach((projectResults, project) => {
-            for (const referencedSymbol of projectResults) {
-                const mappedDefinitionFile = getMappedLocationForProject(documentSpanLocation(referencedSymbol.definition), project);
-                const definition: ReferencedSymbolDefinitionInfo = mappedDefinitionFile === undefined ?
-                    referencedSymbol.definition :
-                    {
-                        ...referencedSymbol.definition,
-                        textSpan: createTextSpan(mappedDefinitionFile.pos, referencedSymbol.definition.textSpan.length), // Why would the length be the same in the original?
-                        fileName: mappedDefinitionFile.fileName,
-                        contextSpan: getMappedContextSpanForProject(referencedSymbol.definition, project)
-                    };
+            if (projectResults) {
+                for (const referencedSymbol of projectResults) {
+                    const mappedDefinitionFile = getMappedLocationForProject(documentSpanLocation(referencedSymbol.definition), project);
+                    const definition: ReferencedSymbolDefinitionInfo = mappedDefinitionFile === undefined ?
+                        referencedSymbol.definition :
+                        {
+                            ...referencedSymbol.definition,
+                            textSpan: createTextSpan(mappedDefinitionFile.pos, referencedSymbol.definition.textSpan.length), // Why would the length be the same in the original?
+                            fileName: mappedDefinitionFile.fileName,
+                            contextSpan: getMappedContextSpanForProject(referencedSymbol.definition, project)
+                        };
 
-                let symbolToAddTo = find(results, o => documentSpansEqual(o.definition, definition));
-                if (!symbolToAddTo) {
-                    symbolToAddTo = { definition, references: [] };
-                    results.push(symbolToAddTo);
-                }
+                    let symbolToAddTo = find(results, o => documentSpansEqual(o.definition, definition));
+                    if (!symbolToAddTo) {
+                        symbolToAddTo = { definition, references: [] };
+                        results.push(symbolToAddTo);
+                    }
 
-                for (const ref of referencedSymbol.references) {
-                    if (!seenRefs.has(ref) && !getMappedLocationForProject(documentSpanLocation(ref), project)) {
-                        seenRefs.add(ref);
-                        symbolToAddTo.references.push(ref);
+                    for (const ref of referencedSymbol.references) {
+                        if (!seenRefs.has(ref) && !getMappedLocationForProject(documentSpanLocation(ref), project)) {
+                            seenRefs.add(ref);
+                            symbolToAddTo.references.push(ref);
+                        }
                     }
                 }
             }
@@ -504,9 +508,9 @@ namespace ts.server {
         isForRename: boolean,
         getResultsForPosition: (project: Project, location: DocumentPosition) => readonly TResult[] | undefined,
         forPositionInResult: (result: TResult, cb: (location: DocumentPosition) => void) => void,
-    ): readonly TResult[] | ESMap<Project, readonly TResult[]> {
+    ): readonly TResult[] | ESMap<Project, undefined | readonly TResult[]> {
         // If `getResultsForPosition` returns results for a project, they go in here
-        const resultsMap = new Map<Project, readonly TResult[]>();
+        const resultsMap = new Map<Project, undefined | readonly TResult[]>();
 
         const queue: ProjectAndLocation[] = [];
 
@@ -588,7 +592,8 @@ namespace ts.server {
         // it easier for the caller to skip post-processing.
         if (resultsMap.size === 1) {
             const it = resultsMap.values().next();
-            return it.done ? emptyArray : it.value; // There may not be any results at all
+            Debug.assert(!it.done);
+            return it.value ?? emptyArray;
         }
 
         return resultsMap;