fix weight by size potential error

lm_eval/evaluator.py

@@ -197,7 +197,6 @@ def evaluate(
     decontamination_ngrams_path=None,
     write_out: bool = False,
     log_samples: bool = True,
-    weight_by_size: bool = False,
 ):
     """Instantiate and evaluate a model on a list of tasks.
 
@@ -485,7 +484,7 @@ def evaluate(
                         if "alias" in metrics:
                             metrics.pop("alias")
 
-                        if configs[task]["weight_by_size"]:
+                        if ("weight_by_size" in configs) and configs[task]["weight_by_size"]:
                             current_size = metrics.pop("samples")
                         else:
                             metrics.pop("samples")