adds missing task error

lm_eval/tasks/__init__.py

+from pprint import pprint
+
 from . import superglue
 from . import glue
 from . import arc
@@ -96,7 +98,12 @@ ALL_TASKS = sorted(list(TASK_REGISTRY))
 
 
 def get_task(task_name):
-    return TASK_REGISTRY[task_name]
+    try:
+        return TASK_REGISTRY[task_name]
+    except KeyError as e:
+        print("Available tasks:")
+        pprint(TASK_REGISTRY)
+        raise KeyError(f"Missing task {task_name}")
 
 
 def get_task_dict(task_name_list):