core/src/main/java/io/fabric8/maven/core/util/MapUtil.java
public static void mergeIfAbsent(Map<String, String> map, Map<String, String> toMerge) {
        for (Map.Entry<String, String> entry : toMerge.entrySet()) {
            putIfAbsent(map, entry.getKey(), entry.getValue());;
        }
    }
public static void mergeIfAbsent(Map<String, String> map, Map<String, String> toMerge) {
        for (Map.Entry<String, String> entry : toMerge.entrySet()) {
            putIfAbsent(map, entry.getKey(), entry.getValue());;
        }
    }
Add all values of a map to another map, but onlfy if not already existing.
@param map target map
@param toMerge the values to ad