lower version, for example 2.6.8
```properties
dubbo.provider.version=1.0
```

2.7.6 failed to recognize the provider url with 'default.version=1.0' key,  it only takes 'version.1.0' into consideration.

if (parameter != null) {
            return parameter;
        }
        return parameter = toParameterString(new String[0]);
    }
    public String toParameterString(String... parameters) {
        StringBuilder buf = new StringBuilder();
        buildParameters(buf, false, parameters);
        return buf.toString();
    }
    private void buildParameters(StringBuilder buf, boolean concat, String[] parameters) {
        if (CollectionUtils.isNotEmptyMap(getParameters())) {
            List<String> includes = (ArrayUtils.isEmpty(parameters) ? null : Arrays.asList(parameters));
            boolean first = true;
            for (Map.Entry<String, String> entry : new TreeMap<>(getParameters()).entrySet()) {
                if (StringUtils.isNotEmpty(entry.getKey())
                        && (includes == null || includes.contains(entry.getKey()))) {
                    if (first) {
                        if (concat) {
                            buf.append("?");
                        }
                        first = false;
                    } else {
                        buf.append("&");
                    }
                    buf.append(entry.getKey());
                    buf.append("=");
                    buf.append(entry.getValue() == null ? "" : entry.getValue().trim());
                }
            }