[Bugfix] Z-Image CFG threshold should be > 0 instead of > 1 (#1634)

Signed-off-by: Lancer <maruixiang6688@gmail.com>

vllm_omni/diffusion/models/z_image/pipeline_z_image.py

@@ -305,7 +305,7 @@ class ZImagePipeline(nn.Module, DiffusionPipelineProfilerMixin):
 
     @property
     def do_classifier_free_guidance(self):
-        return self._guidance_scale > 1
+        return self._guidance_scale > 0
 
     @property
     def joint_attention_kwargs(self):
@@ -365,7 +365,7 @@ class ZImagePipeline(nn.Module, DiffusionPipelineProfilerMixin):
                 Guidance scale as defined in [Classifier-Free Diffusion Guidance](https://arxiv.org/abs/2207.12598).
                 `guidance_scale` is defined as `w` of equation 2. of [Imagen
                 Paper](https://arxiv.org/pdf/2205.11487.pdf). Guidance scale is enabled by setting `guidance_scale >
-                1`. Higher guidance scale encourages to generate images that are closely linked to the text `prompt`,
+                0`. Higher guidance scale encourages to generate images that are closely linked to the text `prompt`,
                 usually at the expense of lower image quality.
             cfg_normalization (`bool`, *optional*, defaults to False):
                 Whether to apply configuration normalization.
@@ -374,7 +374,7 @@ class ZImagePipeline(nn.Module, DiffusionPipelineProfilerMixin):
             negative_prompt (`str` or `list[str]`, *optional*):
                 The prompt or prompts not to guide the image generation. If not defined, one has to pass
                 `negative_prompt_embeds` instead. Ignored when not using guidance (i.e., ignored if `guidance_scale` is
-                less than `1`).
+                less than or equal to `0`).
             num_images_per_prompt (`int`, *optional*, defaults to 1):
                 The number of images to generate per prompt.
             generator (`torch.Generator` or `list[torch.Generator]`, *optional*):