RSCanvas interface, make signature garbage value default ""

src/main/java/net/runelite/mapping/ObfuscatedSignature.java

@@ -11,5 +11,5 @@ public @interface ObfuscatedSignature
 {
 	String signature();
 
-	String garbageValue(); // valid garbage value for last parameter. can't be an Object because Java.
+	String garbageValue() default ""; // valid garbage value for last parameter. can't be an Object because Java.
 }

src/main/java/net/runelite/rs/api/RSCanvas.java

@@ -0,0 +1,5 @@
+package net.runelite.rs.api;
+
+public interface RSCanvas
+{
+}