Index: lldb/include/lldb/Expression/DiagnosticManager.h
===================================================================
--- lldb/include/lldb/Expression/DiagnosticManager.h
+++ lldb/include/lldb/Expression/DiagnosticManager.h
@@ -114,7 +114,8 @@
   }
 
   void AddDiagnostic(std::unique_ptr<Diagnostic> diagnostic) {
-    m_diagnostics.push_back(std::move(diagnostic));
+    if (diagnostic)
+      m_diagnostics.push_back(std::move(diagnostic));
   }
 
   size_t Printf(DiagnosticSeverity severity, const char *format, ...)
Index: lldb/unittests/Expression/DiagnosticManagerTest.cpp
===================================================================
--- lldb/unittests/Expression/DiagnosticManagerTest.cpp
+++ lldb/unittests/Expression/DiagnosticManagerTest.cpp
@@ -75,6 +75,9 @@
 TEST(DiagnosticManagerTest, GetStringNoDiags) {
   DiagnosticManager mgr;
   EXPECT_EQ("", mgr.GetString());
+  std::unique_ptr<Diagnostic> empty;
+  mgr.AddDiagnostic(std::move(empty));
+  EXPECT_EQ("", mgr.GetString());
 }
 
 TEST(DiagnosticManagerTest, GetStringBasic) {