private boolean isFieldType(Set<String> fieldSet, Object builder, String methodName, java.lang.reflect.Type type) {
        String key = fieldKey(builder, methodName);
        if (fieldSet.contains(key)) {
            return true;
        }
        boolean isType = false;
        try {
            Field field = builder.getClass().getDeclaredField(methodName);
            java.lang.reflect.Type fieldType = field.getGenericType();
            if (fieldType instanceof Class<?> && fieldType == type) {
                isType = true;
            } else if (fieldType instanceof ParameterizedType) {
                isType = isParameterizedWith((ParameterizedType) fieldType, type);
            }
        } catch (NoSuchFieldException e) {
        }
        if (isType) {
            fieldSet.add(key);
        }
        return isType;
    }
Checks if this field is of type 'path', in which
case some special handling might be needed. Caches the result.
config/src/main/java/com/yahoo/vespa/config/ConfigPayloadApplier.java