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3.0 gives us the opportunity to make backward-incompatible changes. With that, now is a good time to change the default serde from `byte array` to `null`. This change will allow users to better catch serialization issues from the beginning, as it's likely that they need to be setting a default serde themselves or passing in a serde rather than relying on the byte array default. 

Public Interfaces

Within `StreamsConfig.java`, DEFAULT_KEY_SERDE_CLASS_CONFIG will default to null and DEFAULT_VALUE_SERDE_CLASS_CONFIG will default to null. That means that the following methods will return `null` if no default is set.

// Will return null if no default is set through configs
public Serde defaultKeySerde() {
}

// Will return null if no default is set through configs
 public Serde defaultValueSerde() {
}

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