wro4j-core/src/main/java/ro/isdc/wro/util/WroUtil.java
public static String joinPath(final String left, final String right) {
    String leftHand = left;
    if (!left.endsWith(SEPARATOR_UNIX)) {
      leftHand += SEPARATOR_UNIX;
    }
    return leftHand + right.replaceFirst("^/(.*)", "$1");
  }
public static String joinPath(final String left, final String right) {
    String leftHand = left;
    if (!left.endsWith(SEPARATOR_UNIX)) {
      leftHand += SEPARATOR_UNIX;
    }
    return leftHand + right.replaceFirst("^/(.*)", "$1");
  }
Join two paths (using unix separator) and make sure to use exactly one separator (by adding or removing one if required).