protected Ini resolveIni() {
        Ini ini = getIni();
        if (CollectionUtils.isEmpty(ini)) {
            LOGGER.debug("Null or empty Ini instance.  Falling back to the default {} file.", DEFAULT_INI_RESOURCE_PATH);
            ini = loadDefaultClassPathIni();
        }
        return ini;
    }
Tries to resolve the Ini instance to use for configuration.  This implementation functions as follows:
<ol>
<li>The {@code Ini} instance returned from {@link #getIni()} will be returned if it is not null or empty.</li>
<li>If {@link #getIni()} is {@code null} or empty, this implementation will attempt to find and load the
{@link #loadDefaultClassPathIni() default class path Ini}.</li>
<li>If neither of the two attempts above returns an instance, {@code null} is returned</li>
</ol>

@return the Ini instance to use for configuration.
core/src/main/java/org/apache/shiro/ini/IniFactorySupport.java