fix nan to num inverse

Author: arrjon

bayesflow/adapters/transforms/nan_to_num.py

@@ -80,6 +80,8 @@ def inverse(self, data: dict[str, any], **kwargs) -> dict[str, any]:
  data = data.copy()
 
  # Retrieve mask and values to reconstruct NaNs
+ if self.key not in data.keys():
+ return data
  values = data[self.key]
 
  if not self.return_mask: