Fix empty sketch issue

app.py

@@ -137,7 +137,6 @@ class ServingCommand(object):
 
 def build_gradio_app(queues, command):
     """Build the gradio application."""
-    import cv2
     import gradio as gr
     import gradio_image_prompter as gr_ext
 
@@ -186,12 +185,14 @@ def build_gradio_app(queues, command):
             img, points = mask_img["background"], []
             for layer in mask_img["layers"]:
                 ys, xs = np.nonzero(layer[:, :, 0])
-                keep = np.linspace(0, ys.shape[0], 11, dtype="int64")[1:-1]
-                points.append(np.stack([xs[keep][None, :], ys[keep][None, :]], 2))
-            points = np.concatenate(points).astype("float32")
-            points = np.pad(points, [(0, 0), (0, 0), (0, 1)], constant_values=1)
-            pad_points = np.array([[[0, 0, 4]]], "float32").repeat(points.shape[0], 0)
-            points = np.concatenate([points, pad_points], axis=1)
+                if len(ys) > 0:
+                    keep = np.linspace(0, ys.shape[0], 11, dtype="int64")[1:-1]
+                    points.append(np.stack([xs[keep][None, :], ys[keep][None, :]], 2))
+            if len(points) > 0:
+                points = np.concatenate(points).astype("float32")
+                points = np.pad(points, [(0, 0), (0, 0), (0, 1)], constant_values=1)
+                pad_points = np.array([[[0, 0, 4]]], "float32").repeat(points.shape[0], 0)
+                points = np.concatenate([points, pad_points], axis=1)
         img = img[:, :, (2, 1, 0)] if img is not None else img
         img = np.zeros((480, 640, 3), dtype="uint8") if img is None else img
         points = (np.array([[[0, 0, 4]]]) if len(points) == 0 else points).astype("float32")