Follow-up fix wrt #4783: prevent too early fail on abstract Map types (#4794)

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/deser/BasicDeserializerFactory.java

@@ -968,13 +968,9 @@ public JsonDeserializer<?> createMapDeserializer(DeserializationContext ctxt,
                         mapClass = type.getRawClass();
                         // But if so, also need to re-check creators...
                         beanDesc = config.introspectForCreation(type);
-                    } else {
-                        // [databind#292]: Actually, may be fine, but only if polymorphic deser enabled
-                        if (type.getTypeHandler() == null) {
-                            throw new IllegalArgumentException("Cannot find a deserializer for non-concrete Map type "+type);
-                        }
-                        deser = AbstractDeserializer.constructForNonPOJO(beanDesc);
                     }
+                    // 11-Nov-2024, tatu: Related to [databind#4783] let's not fail on
+                    //    abstract Maps so they can work with merge (or factory methods)
                 } else {
                     // 10-Jan-2017, tatu: `java.util.Collections` types need help:
                     deser = JavaUtilCollectionsDeserializers.findForMap(ctxt, type);