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

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

Index: pkg/analyzer/lib/src/generated/resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/resolver.dart b/pkg/analyzer/lib/src/generated/resolver.dart
index f709d561fd01fbaee3309b95f92c615b2c09aeff..6d7f6e9f7d12da8f98ddc7679a1df603dd982192 100644
--- a/pkg/analyzer/lib/src/generated/resolver.dart
+++ b/pkg/analyzer/lib/src/generated/resolver.dart
@@ -8435,7 +8435,11 @@ class ResolverVisitor extends ScopedVisitor {
       }
     } else {
       // TODO(leafp): Do downwards inference using the declared type
-      // of the binary operator.
+      // of the binary operator for other cases.
+      if (operatorType == TokenType.QUESTION_QUESTION) {
+        InferenceContext.setTypeFromNode(leftOperand, node);
+        InferenceContext.setTypeFromNode(rightOperand, node);
+      }
       safelyVisit(leftOperand);
       safelyVisit(rightOperand);
     }