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WithKeys
--------

**Kata:** Convert each fruit name into a KV of its first letter and itself, e.g. 
`apple => KV.of("a", "apple")`

<div class="hint">
  Use <a href="https://beam.apache.org/releases/javadoc/current/org/apache/beam/sdk/transforms/WithKeys.html">
  WithKeys</a>.
</div>

<div class="hint">
  If using a lambda in Java 8, <code>withKeyType(TypeDescriptor)</code> must be called on the
  result PTransform.
</div>
