fuction walkAST.js

function walkAST(ast, before, after, options){
	
	parents.unshift(ast);

    switch (ast.type) {
	    case 'NamedBlock':
	    case 'Block':
	      ast.nodes = walkAndMergeNodes(ast.nodes);
	      break;
	    case 'Case':
	    case 'Filter':
	    case 'Mixin':
	    case 'Tag':
	    case 'InterpolatedTag':
	    case 'When':
	    case 'Code':
	    case 'While':
	      if (ast.block) { // here!!!
	        ast.block = walkAST(ast.block, before, after, options);
	      }
	      break;
	    case 'Text':
	      break;
	}
	parents.shift();

}