Panic when Context.lookup returns 0

src/context.zig

@@ -15,7 +15,9 @@ pub fn Context(comptime ctx: anytype) type {
         /// type that has been registered previously, typically done by
         /// calling functions such as `World.component(...)`.
         pub fn lookup(comptime T: type) c.ecs_entity_t {
-            return lookupMut(T).*;
+            const result = lookupMut(T).*;
+            if (result == 0) std.debug.panic("No lookup for {s}", .{@typeName(T)});
+            return result;
         }
 
         /// Returns a pointer unique to this `Context` and the provided type