Unknown flag: --builder with docker buildx

[pchaigno]

I'm getting an unknown flag: --builder if I try to build an image with the latest version. I'm using the Buildx plugin included in the Docker CLI, after enabling experimental features as per the documentation.

$ docker --version
Docker version 19.03.12, build 48a66213fe
$ PUSH=true REGISTRIES=docker.io/pchaigno make llvm-image 
PUSH=true EXPORT=false TEST=true scripts/build-image.sh cilium-llvm images/llvm linux/amd64 "$(cat .buildx_builder)" docker.io/pchaigno
will build cilium-llvm:76897177401ee8c204b160bfb154bcc67409b885-wip as it has wip suffix
building cilium-llvm:76897177401ee8c204b160bfb154bcc67409b885-wip
+ run_buildx
+ build_args=("--platform=${platform}" "--builder=${builder}" "--file=${image_dir}/Dockerfile")
+ '[' false = false ']'
+ build_args+=("${image_dir}")
+ '[' true = true ']'
+ docker buildx build --target=test --platform=linux/amd64 --builder= --file=images/llvm/Dockerfile images/llvm
unknown flag: --builder
See 'docker buildx build --help'.
+ exit 1
make: *** [Makefile:53: llvm-image] Error 1

If I remove that flag as follows, everything works fine.

diff --git a/scripts/build-image.sh b/scripts/build-image.sh
index 0504afa..fa16228 100755
--- a/scripts/build-image.sh
+++ b/scripts/build-image.sh
@@ -114,7 +114,6 @@ do_test="${TEST:-false}"
 run_buildx() {
   build_args=(
     "--platform=${platform}"
-    "--builder=${builder}"
     "--file=${image_dir}/Dockerfile"
   )
   if [ "${with_root_context}" = "false" ] ; then

Should I be using a different Docker version?