Empty, guarded mixin is zeroing out other mixins under the same rule

[johnnywang]

I've been trying to get the following guarded mixins to work correctly in our LESS stylesheets:

font {

.body( @size: 15px, @lineHeight: 18px, @weight: normal ) {
    font: @weight @size~"/"@lineHeight Arial, sans-serif;
}
.marginLeft( @margin ) when ( @margin = 0 ) { }
.marginLeft( @margin ) when not ( @margin = 0 ) {
    margin-left: @margin;
}
.marginTop( @margin ) when ( @margin = 0 ) { }
.marginTop( @margin ) when not ( @margin = 0 ) {
    margin-top: @margin;
}
.DinBold( @size: 14px, @lineHeight: 20px, @offsetTop: 0, @offsetLeft: 0 ) {
    #font > .marginLeft( @offsetLeft );
    #font > .marginTop( @offsetTop );
    font: @size~"/"@lineHeight 'DINBold', Arial, sans-serif;
}

}

The idea here being that if any of the font offsets are zero, I don't want the margin style to be set. Now, it works fine when the two parameters are non-zero, like:

font > .DinBold( 42px, 42px, -7px, -3px );

But the moment @offsetLeft is 0, either explicitly or implicitly:

font > .DinBold( 42px, 42px, -7px );

or

font > .DinBold( 42px, 42px, -7px, 0 );

it seems that even the margin-top won't be exposed. The same thing happens if you flip it around, putting the marginTop mixin before the marginLeft mixin, and passing in 0 for @offsetTop instead, which seems to suggest to me that the first time an empty mixin is hit, all subsequent mixin calls might be ignored.

[lukeapage]

when a empty mixin is hit and the next rule is a call to a mixin, that next rule was being ignored.

This is now fixed and will be in the next release.