Fix #4336 - don’t merge sources twice for null coalesce

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

@@ -1273,14 +1273,6 @@ class AssignmentAnalyzer
                 $statements_analyzer->node_data->setType($stmt, $fake_coalesce_type);
             }
 
-            BinaryOpAnalyzer::addDataFlow(
-                $statements_analyzer,
-                $stmt,
-                $stmt->var,
-                $stmt->expr,
-                'coalesce'
-            );
-
             return true;
         }
 

tests/UnusedVariableTest.php

@@ -2188,6 +2188,14 @@ class UnusedVariableTest extends TestCase
                         print_r(...func_get_args());
                     }'
             ],
+            'nullCoalesce' => [
+                '<?php
+                    function foo (?bool $b, int $c): void {
+                        $b ??= $c;
+
+                        echo $b;
+                    }'
+            ],
         ];
     }