Address CR feedback

src/compiler/binder.ts

@@ -1,3 +1,4 @@
+
 /* @internal */
 namespace ts {
     export const enum ModuleInstanceState {
@@ -953,7 +954,7 @@ namespace ts {
             }
             if ((expression.kind === SyntaxKind.TrueKeyword && flags & FlowFlags.FalseCondition ||
                 expression.kind === SyntaxKind.FalseKeyword && flags & FlowFlags.TrueCondition) &&
-                !isExpressionOfOptionalChainRoot(expression) && !isQuestionQuestionExpression(expression.parent)) {
+                !isExpressionOfOptionalChainRoot(expression) && !isNullishCoalesce(expression.parent)) {
                 return unreachableFlow;
             }
             if (!isNarrowingExpression(expression)) {

src/compiler/utilities.ts

@@ -5953,7 +5953,7 @@ namespace ts {
         return isOptionalChainRoot(node.parent) && node.parent.expression === node;
     }
 
-    export function isQuestionQuestionExpression(node: Node) {
+    export function isNullishCoalesce(node: Node) {
         return node.kind === SyntaxKind.BinaryExpression && (<BinaryExpression>node).operatorToken.kind === SyntaxKind.QuestionQuestionToken;
     }