checking and inference of null coalescing operator, fixes #24564 and fixes #25387

pkg/analyzer/lib/src/generated/static_type_analyzer.dart

Index: pkg/analyzer/lib/src/generated/static_type_analyzer.dart
diff --git a/pkg/analyzer/lib/src/generated/static_type_analyzer.dart b/pkg/analyzer/lib/src/generated/static_type_analyzer.dart
index b8ab670f240b18777c5054a989d9c631688a8112..28f42f74b199ec679e8bf7b4900c57e3f325ef50 100644
--- a/pkg/analyzer/lib/src/generated/static_type_analyzer.dart
+++ b/pkg/analyzer/lib/src/generated/static_type_analyzer.dart
@@ -330,7 +330,7 @@ class StaticTypeAnalyzer extends SimpleAstVisitor<Object> {
   @override
   Object visitBinaryExpression(BinaryExpression node) {
     if (node.operator.type == TokenType.QUESTION_QUESTION) {
-      // Evaluation of an if-null expresion e of the form e1 ?? e2 is
+      // Evaluation of an if-null expression e of the form e1 ?? e2 is
       // equivalent to the evaluation of the expression
       // ((x) => x == null ? e2 : x)(e1).  The static type of e is the least
       // upper bound of the static type of e1 and the static type of e2.