fix z-image non-diffusers lora loading.

src/diffusers/loaders/lora_conversion_utils.py

@@ -2538,8 +2538,12 @@ def _convert_non_diffusers_z_image_lora_to_diffusers(state_dict):
 
     def get_alpha_scales(down_weight, alpha_key):
         rank = down_weight.shape[0]
-        alpha = state_dict.pop(alpha_key).item()
-        scale = alpha / rank  # LoRA is scaled by 'alpha / rank' in forward pass, so we need to scale it back here
+        alpha_tensor = state_dict.pop(alpha_key, None)
+        if alpha_tensor is None:
+            return 1.0, 1.0
+        scale = (
+            alpha_tensor.item() / rank
+        )  # LoRA is scaled by 'alpha / rank' in forward pass, so we need to scale it back here
         scale_down = scale
         scale_up = 1.0
         while scale_down * 2 < scale_up: