Repro bug in ConcretizeStaticInheritanceForInlining

It's copying seemingly random static properties to other classes in some cases, because of a bug around Java null.

PiperOrigin-RevId: 554520757

test/com/google/javascript/jscomp/ConcretizeStaticInheritanceForInliningTest.java

@@ -625,4 +625,37 @@ public void testAddSingletonGetter() {
             "$jscomp.inherits(Subclass, Example);",
             "goog.addSingletonGetter(Subclass);"));
   }
+
+  @Test
+  public void testNonQnameConstructor_doesntPolluteListOfAssignments() {
+    // Reproduce a pretty bad bug caused by accidentally reading/writing 'null' keys from a map.
+    test(
+        lines(
+            "const ns = {};",
+            "/** @constructor */",
+            "ns['NOT_A_NAME'] = function() {};",
+            "ns['NOT_A_NAME'].staticMethod = function() { alert(1); }",
+            "",
+            "/** @constructor */",
+            "const Example = function() {}",
+            "",
+            "/** @constructor @extends {Example} */",
+            "function Subclass() {}",
+            "$jscomp.inherits(Subclass, Example);"),
+        lines(
+            "const ns = {};",
+            "/** @constructor */",
+            "ns['NOT_A_NAME'] = function() {};",
+            "ns['NOT_A_NAME'].staticMethod = function() { alert(1); }",
+            "",
+            "/** @constructor */",
+            "const Example = function() {}",
+            "",
+            "/** @constructor @extends {Example} */",
+            "function Subclass() {}",
+            "$jscomp.inherits(Subclass, Example);",
+            // TODO(b/293320792) - stop producing this assignment, there's no
+            // actual Example.staticMethod.
+            "Subclass.staticMethod = Example.staticMethod;"));
+  }
 }