[NFC] Fix potential dereferencing of nullptr

Differential Revision: https://reviews.llvm.org/D139148

clang/lib/Sema/SemaInit.cpp

@@ -6336,6 +6336,7 @@ void InitializationSequence::InitializeFrom(Sema &S,
   // We're at the end of the line for C: it's either a write-back conversion
   // or it's a C assignment. There's no need to check anything else.
   if (!S.getLangOpts().CPlusPlus) {
+    assert(Initializer && "Initializer must be non-null");
     // If allowed, check whether this is an Objective-C writeback conversion.
     if (allowObjCWritebackConversion &&
         tryObjCWritebackConversion(S, *this, Entity, Initializer)) {
@@ -6362,7 +6363,8 @@ void InitializationSequence::InitializeFrom(Sema &S,
     if (Kind.getKind() == InitializationKind::IK_Direct ||
         (Kind.getKind() == InitializationKind::IK_Copy &&
          (Context.hasSameUnqualifiedType(SourceType, DestType) ||
-          S.IsDerivedFrom(Initializer->getBeginLoc(), SourceType, DestType)))) {
+          (Initializer && S.IsDerivedFrom(Initializer->getBeginLoc(),
+                                          SourceType, DestType))))) {
       TryConstructorInitialization(S, Entity, Kind, Args, DestType, DestType,
                                    *this);
 
@@ -6406,6 +6408,7 @@ void InitializationSequence::InitializeFrom(Sema &S,
       //       function is used) to a derived class thereof are enumerated as
       //       described in 13.3.1.4, and the best one is chosen through
       //       overload resolution (13.3).
+      assert(Initializer && "Initializer must be non-null");
       TryUserDefinedConversion(S, DestType, Kind, Initializer, *this,
                                TopLevelOfInitList);
     }
@@ -6457,6 +6460,7 @@ void InitializationSequence::InitializeFrom(Sema &S,
   //    - Otherwise, if the source type is a (possibly cv-qualified) class
   //      type, conversion functions are considered.
   if (!SourceType.isNull() && SourceType->isRecordType()) {
+    assert(Initializer && "Initializer must be non-null");
     // For a conversion to _Atomic(T) from either T or a class type derived
     // from T, initialize the T object then convert to _Atomic type.
     bool NeedAtomicConversion = false;