Fix #2677 - use better assertion for null coalesce

Author: muglug

src/Psalm/Internal/Analyzer/Statements/Expression/BinaryOpAnalyzer.php

@@ -778,7 +778,7 @@ function (\Psalm\Internal\Clause $c) use ($mixed_var_ids) {
 
             if ($stmt_left_type = $statements_analyzer->node_data->getType($stmt->left)) {
                 $if_return_type_reconciled = AssertionReconciler::reconcile(
-                    '!null',
+                    'isset',
                     clone $stmt_left_type,
                     '',
                     $statements_analyzer,

tests/AnnotationTest.php

@@ -1061,6 +1061,16 @@ function foo(array $_bar) : void { }
                     /** @param list<scalar|array|object|resource|null> $_s */
                     function foo(array $_s) : void { }'
             ],
+            'possiblyUndefinedObjectProperty' => [
+                '<?php
+                    function consume(string $value): void {
+                      echo $value;
+                    }
+
+                    /** @var object{value?: string} $data */
+                    $data = json_decode("{}", false);
+                    consume($data->value ?? "");'
+            ],
         ];
     }