diff --git a/src/test/java/toolbox/Main.java b/src/test/java/toolbox/Main.java
index c30dcbf..f74f56b 100644
--- a/src/test/java/toolbox/Main.java
+++ b/src/test/java/toolbox/Main.java
@@ -2,6 +2,7 @@ package toolbox;
 
 import org.junit.jupiter.api.Test;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
 
@@ -14,6 +15,7 @@ public class Main {
 	static native String concat(String a, String b);
 	static native String[] to_vec(String a, String b, String c);
 	static native boolean maybe(String optional);
+	static native String optional(boolean present);
 	static native String raw();
 
 	@Test
@@ -29,9 +31,9 @@ public class Main {
 	@Test
 	public void checksForNull() {
 		// TODO maybe these should throw NullPtrException
-		assertThrows(RuntimeException.class, () -> Main.concat("a", null));
-		assertThrows(RuntimeException.class, () -> Main.concat(null, "a"));
-		assertThrows(RuntimeException.class, () -> Main.concat(null, null));
+		assertThrows(NullPointerException.class, () -> Main.concat("a", null));
+		assertThrows(NullPointerException.class, () -> Main.concat(null, "a"));
+		assertThrows(NullPointerException.class, () -> Main.concat(null, null));
 	}
 
 	@Test
@@ -53,5 +55,11 @@ public class Main {
 	public void passEnv() {
 		assertEquals(Main.raw(), "hello world!");
 	}
+
+	@Test
+	public void nullableReturn() {
+		assertNull(Main.optional(false));
+		assertEquals(Main.optional(true), "hello world!");
+	}
 	
 }
diff --git a/src/test/test.rs b/src/test/test.rs
index ab10f52..4780982 100644
--- a/src/test/test.rs
+++ b/src/test/test.rs
@@ -20,6 +20,15 @@ fn maybe(idk: Option<String>) -> bool {
 	idk.is_some()
 }
 
+#[jni(package = "toolbox", class = "Main")]
+fn optional(present: bool) -> Option<String> {
+	if present {
+		Some("hello world!".into())
+	} else {
+		None
+	}
+}
+
 #[jni(package = "toolbox", class = "Main")]
 fn raw<'local>(env: &mut jni::JNIEnv<'local>) -> Result<jni::objects::JString<'local>, jni::errors::Error> {
 	env.new_string("hello world!")