修复空指针问题

src/main/java/org/redkale/source/CacheMemorySource.java

@@ -79,7 +79,8 @@ public final class CacheMemorySource extends AbstractCacheSource {
     }
 
     public static boolean acceptsConf(AnyValue config) {
-        return config.getValue(CACHE_SOURCE_NODES).startsWith("memory:");
+        String nodes = config.getValue(CACHE_SOURCE_NODES);
+        return nodes != null && nodes.startsWith("memory:");
     }
 
     @Override