Update controlnet_flux.py (#11350)

src/diffusers/models/controlnets/controlnet_flux.py

@@ -430,7 +430,7 @@ class FluxMultiControlNetModel(ModelMixin):
     ) -> Union[FluxControlNetOutput, Tuple]:
         # ControlNet-Union with multiple conditions
         # only load one ControlNet for saving memories
-        if len(self.nets) == 1 and self.nets[0].union:
+        if len(self.nets) == 1:
             controlnet = self.nets[0]
 
             for i, (image, mode, scale) in enumerate(zip(controlnet_cond, controlnet_mode, conditioning_scale)):
@@ -454,11 +454,12 @@ class FluxMultiControlNetModel(ModelMixin):
                     control_block_samples = block_samples
                     control_single_block_samples = single_block_samples
                 else:
+                    if block_samples is not None and control_block_samples is not None:
                         control_block_samples = [
                             control_block_sample + block_sample
                             for control_block_sample, block_sample in zip(control_block_samples, block_samples)
                         ]
-
+                    if single_block_samples is not None and control_single_block_samples is not None:
                         control_single_block_samples = [
                             control_single_block_sample + block_sample
                             for control_single_block_sample, block_sample in zip(