Added default duration of zero

Tests/test_file_webp.py

@@ -8,6 +8,7 @@
 from PIL import Image, WebPImagePlugin, features
 
 from .helper import (
+    assert_image_equal,
     assert_image_similar,
     assert_image_similar_tofile,
     hopper,
@@ -105,6 +106,18 @@ def test_write_method(self, tmp_path):
         hopper().save(buffer_method, format="WEBP", method=6)
         assert buffer_no_args.getbuffer() != buffer_method.getbuffer()
 
+    def test_save_all(self, tmp_path):
+        temp_file = str(tmp_path / "temp.webp")
+        im = Image.new("RGB", (1, 1))
+        im2 = Image.new("RGB", (1, 1), "#f00")
+        im.save(temp_file, save_all=True, append_images=[im2])
+
+        with Image.open(temp_file) as reloaded:
+            assert_image_equal(im, reloaded)
+
+            reloaded.seek(1)
+            assert_image_similar(im2, reloaded, 1)
+
     def test_icc_profile(self, tmp_path):
         self._roundtrip(tmp_path, self.rgb_mode, 12.5, {"icc_profile": None})
         if _webp.HAVE_WEBPANIM:

src/PIL/WebPImagePlugin.py

@@ -192,7 +192,7 @@ def _save_all(im, fp, filename):
                 r, g, b = palette[background * 3 : (background + 1) * 3]
                 background = (r, g, b, 0)
 
-    duration = im.encoderinfo.get("duration", im.info.get("duration"))
+    duration = im.encoderinfo.get("duration", im.info.get("duration", 0))
     loop = im.encoderinfo.get("loop", 0)
     minimize_size = im.encoderinfo.get("minimize_size", False)
     kmin = im.encoderinfo.get("kmin", None)