The border-image shorthand was incorrectly parsed as an empty value

[yisibl]

input

.test1 {
  border-image: none;
  border-image-source: unknow;
}

.test2 {
  border-image: none;
  border-image-repeat: unknow;
}

output

lightningcss 1.31.1

test1 {
  border-image: ;
  border-image-source: unknow;
}

.test2 {
  border-image: ;
  border-image-repeat: unknow;
}