- fix: NullPointerException when the config class of mod updated

- alter: better test code in `common/src/test`, `neoforge/src/test` and `fabric/src/test`, run `Test Minecraft Client(:fabric)` or `Test Minecraft Client(:neoforge)` for testing

fabric/src/test/resources/fabric.mod.json

@@ -0,0 +1,23 @@
+{
+    "schemaVersion": 1,
+    "id": "modid",
+    "version": "${version}",
+
+    "name": "MidnightLib Test Mod",
+    "description": "Example Mod for Team MidnightDust's mods.",
+    "authors": [ "MidnightDust" ],
+
+    "license": "CC0",
+    "icon": "assets/midnightlib/icon.png",
+
+    "environment": "*",
+    "entrypoints": {
+        "main": [
+            "eu.midnightdust.test.fabric.MLExampleFabric"
+        ]
+    },
+    "depends": {
+        "fabric-resource-loader-v0": "*",
+        "midnightlib": ">=1.6.0"
+    }
+}