Use null-aware operators to clean up the code

pkg/analyzer/lib/src/dart/ast/utilities.dart

Index: pkg/analyzer/lib/src/dart/ast/utilities.dart
diff --git a/pkg/analyzer/lib/src/dart/ast/utilities.dart b/pkg/analyzer/lib/src/dart/ast/utilities.dart
index a87c085386de557a0b5d861bd7726f0006ea8e2c..cde48256503cf6db6ad464f302aff23eddd68da5 100644
--- a/pkg/analyzer/lib/src/dart/ast/utilities.dart
+++ b/pkg/analyzer/lib/src/dart/ast/utilities.dart
@@ -3679,7 +3679,7 @@ class NodeLocator extends UnifyingAstVisitor<Object> {
    */
   NodeLocator(int startOffset, [int endOffset])
       : this._startOffset = startOffset,
-        this._endOffset = endOffset == null ? startOffset : endOffset;
+        this._endOffset = endOffset ?? startOffset;
 
   /**
    * Return the node that was found that corresponds to the given source range
@@ -3783,7 +3783,7 @@ class NodeLocator2 extends UnifyingAstVisitor<Object> {
    */
   NodeLocator2(int startOffset, [int endOffset])
       : this._startOffset = startOffset,
-        this._endOffset = endOffset == null ? startOffset : endOffset;
+        this._endOffset = endOffset ?? startOffset;
 
   /**
    * Search within the given AST [node] and return the node that was found,