STORM-2548 replaced the KafkaSpoutConfig.builder() implementations with ones that don't set the key/value deserializer fields in KafkaSpoutConfig, but instead just sets the corresponding property in the kafkaProps map. This is a breaking change for applications that assume those properties are set after the builder is created.
Code like the following would break.
this.keyDeserializer = config.getKeyDeserializer().getClass();
this.valueDeserializer = config.getValueDeserializer().getClass();