diff --git a/clang-tools-extra/clangd/Protocol.cpp b/clang-tools-extra/clangd/Protocol.cpp
--- a/clang-tools-extra/clangd/Protocol.cpp
+++ b/clang-tools-extra/clangd/Protocol.cpp
@@ -560,11 +560,13 @@
 }
 
 llvm::json::Value toJSON(const PublishDiagnosticsParams &PDP) {
-  return llvm::json::Object{
+  llvm::json::Object Result{
       {"uri", PDP.uri},
       {"diagnostics", PDP.diagnostics},
-      {"version", PDP.version},
   };
+  if (PDP.version)
+    Result["version"] = PDP.version;
+  return std::move(Result);
 }
 
 bool fromJSON(const llvm::json::Value &Params, CodeActionContext &R) {
diff --git a/clang-tools-extra/clangd/test/diagnostics-no-tidy.test b/clang-tools-extra/clangd/test/diagnostics-no-tidy.test
--- a/clang-tools-extra/clangd/test/diagnostics-no-tidy.test
+++ b/clang-tools-extra/clangd/test/diagnostics-no-tidy.test
@@ -32,8 +32,7 @@
 #      CHECK:  "method": "textDocument/publishDiagnostics",
 # CHECK-NEXT:  "params": {
 # CHECK-NEXT:    "diagnostics": [],
-# CHECK-NEXT:    "uri": "file://{{.*}}/foo.c",
-# CHECK-NEXT:    "version": null
+# CHECK-NEXT:    "uri": "file://{{.*}}/foo.c"
 # CHECK-NEXT:  }
 ---
 {"jsonrpc":"2.0","id":5,"method":"shutdown"}
diff --git a/clang-tools-extra/clangd/test/diagnostics.test b/clang-tools-extra/clangd/test/diagnostics.test
--- a/clang-tools-extra/clangd/test/diagnostics.test
+++ b/clang-tools-extra/clangd/test/diagnostics.test
@@ -48,8 +48,7 @@
 #      CHECK:  "method": "textDocument/publishDiagnostics",
 # CHECK-NEXT:  "params": {
 # CHECK-NEXT:    "diagnostics": [],
-# CHECK-NEXT:    "uri": "file://{{.*}}/foo.c",
-# CHECK-NEXT:    "version": null
+# CHECK-NEXT:    "uri": "file://{{.*}}/foo.c"
 # CHECK-NEXT:  }
 ---
 {"jsonrpc":"2.0","id":5,"method":"shutdown"}