Test invalid deserializer in node helper

src/test/java/com/clubobsidian/wrappy/test/helper/NodeHelperTest.java

@@ -0,0 +1,22 @@
+package com.clubobsidian.wrappy.test.helper;
+
+import static org.junit.Assert.assertTrue;
+
+import java.io.File;
+
+import org.junit.Test;
+import org.spongepowered.configurate.ConfigurationNode;
+
+import com.clubobsidian.wrappy.Configuration;
+import com.clubobsidian.wrappy.helper.NodeHelper;
+
+public class NodeHelperTest {
+
+	@Test
+	public void testInvalid() {
+		Configuration config = Configuration.load(new File("test.yml"));
+		ConfigurationNode node = config.getNode();
+		NodeHelper<Double> helper = new NodeHelper<>(node);
+		assertTrue(helper.get("key", Double.class) == null);
+	}
+}