public String get(String key) {
        JsonElement value = configStorage.get(key);
        if (value == null) {
            LOGGER.error("null value for key " + key);
            throw new NullPointerException("null value for key " + key);
        }
        return value.getAsString();
    }
get string or throw npe

@param key key
@return string
@throws NullPointerException if value is null, throw npe
inlong-agent/agent-common/src/main/java/org/apache/inlong/agent/conf/AbstractConfiguration.java