[SonarLint]: make this anonymous inner class a lambda

The below code works, but I have notification from SonarLint because I use an anonymous class in stream instead of lambda expression, and I don't see how to improve the below code avoiding the notification:

Properties prop = new Properties();
Properties temp = new Properties();
//... add some values and keys in prop and temp

prop.putAll(temp.entrySet().stream()
    .filter( entry -> !prop.containsKey(entry.getKey()))
    .map( new Function<Entry<Object, Object>, Entry<String, String>>(){ 
        @Override
        public Entry<String, String> apply(Entry<Object, Object> entry) {
            return new Entry<String, String>() {
                @Override
                public String setValue(String value) {
                    return value.trim().toLowerCase();
                }

                @Override
                public String getValue() {
                    return ((String) entry.getValue()).trim().toLowerCase();
                }

                @Override
                public String getKey() {
                    return ((String) entry.getKey()).trim().toLowerCase();
                }
            };
        }
    })
    .collect(Collectors.toMap(Entry<String,String>::getKey, Entry<String,String>::getValue)));

Explication of code: I use the properties class from java.util and unfortunately, the entrySet of properties returns Entry<Object, Object>, not Entry<String, String>. I want to "join" the two properties objects putting key and value in lower case. So, the map allows to convert Entry<Object, Object> in Entry<String,String>. That's why, there is an anonymous class.