i think it's from this block

Object dynamicConfigProviderJson = consumerProperties.get(KafkaSupervisorIOConfig.DRUID_DYNAMIC_CONFIG_PROVIDER_KEY);
    if (dynamicConfigProviderJson != null) {
      DynamicConfigProvider dynamicConfigProvider = configMapper.convertValue(dynamicConfigProviderJson, DynamicConfigProvider.class);
      Map<String, String> dynamicConfig = dynamicConfigProvider.getConfig();
      for (Map.Entry<String, String> e : dynamicConfig.entrySet()) {
        properties.setProperty(e.getKey(), e.getValue());
      }
    }

so, there's some null key or value in the dynamic config provided by

druid.dynamic.config.provider

i see there's no nice error message for that case; would be good to add one!