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.

}
    @Override
    public String toString() {
        if (string != null) {
            return string;
        }
        return string = buildString(false, true); 
    }
    public String toString(String... parameters) {
        return buildString(false, true, parameters); 
    }
    public String toIdentityString() {
        if (identity != null) {
            return identity;
        }
        return identity = buildString(true, false); 
    }
    public String toIdentityString(String... parameters) {
        return buildString(true, false, parameters); 
    }
    public String toFullString() {
        if (full != null) {
            return full;
        }
        return full = buildString(true, true);
    }
    public String toFullString(String... parameters) {
        return buildString(true, true, parameters);
    }
    public String toParameterString() {