LESS svg-gradient() function with multiple variables - less

Question

I cannot seem to send multiple variables to the svg-gradient() function in less.
If I don't use variables, the svg-gradient function works fine. (Except for the non-increment of ids - but that's something else entirely!) Or if I send the exact same data to the CSS property, linear-gradient(), which is the same format that the svg-gradient() function requires, it works also.
Can anyone tell me why the commented lines in the code below are not successfully compiling when the ones above and below are succesful?
/* Example 1 */
.my-mixin-gradient(#size: contain; #direction: to right; #color...){
background: svg-gradient(#direction, red 0, orange 20%, yellow 30%, green 50%, blue 70%, indigo 85%, violet 100%);
/* background: svg-gradient(#direction, #color); */ /* Why does this not compile ??? */
background: linear-gradient(#direction, #color);
background-size: #size;
}
.my-class{
.my-mixin-gradient(contain; to bottom; red 0, orange 20%, yellow 30%, green 50%, blue 70%, indigo 85%, violet 100%);
}
/* Example 2 */
.my-mixin-gradient2(#size: contain; #mygrad: to right, #000 0, #fff 100%){
background: svg-gradient(to bottom, #ff0000 0, #ffa500 20%, #ffff00 30%, #008000 50%, #0000ff 70%, #4b0082 85%, #ee82ee 100%);
/* background: svg-gradient(#mygrad); */ /* Why does this not compile either ??? */
background: linear-gradient(#mygrad);
background-size: #size;
}
.my-class2{
.my-mixin-gradient2(contain; to bottom, #ff0000 0, #ffa500 20%, #ffff00 30%, #008000 50%, #0000ff 70%, #4b0082 85%, #ee82ee 100%);
}