LazyHeaderFactory (library 4.14.2 API)

```
public interface LazyHeaderFactory
```
An interface for lazily creating headers that allows expensive to calculate headers (oauth for example) to be generated in the background during the first fetch.
Implementations should implement equals() and hashcode() .

- Method Summary
  
  All Methods Instance Methods Abstract Methods
  Modifier and Type Method Description
  
  java.lang.String buildHeader()
  Returns an http header, or null if no header could be built.

- Method Detail
  - buildHeader
```
@Nullable
java.lang.String buildHeader()
```
    Returns an http header, or null if no header could be built.
    Returning null or an empty String from this method will result in this particular key/value being excluded from the headers provided in the request. If there are multiple factories or values for a particular key, any non-null values will still be included for that key.