False positive: NULL_DEREFERENCE for Drift

Infer version v0.13.0-4488ab099
repo: https://github.com/airlift/drift
commit: `ec21ec853535ccbbfea74a8981da97b81b68b3c0`

```
drift-codec/src/main/java/io/airlift/drift/codec/ThriftCodecManager.java:131: error: NULL_DEREFERENCE
object returned by `type.getKeyTypeReference()` could be null and is dereferenced by call to `getElementCodec(...)` at line 131.
129. return factory.generateThriftTypeCodec(ThriftCodecManager.this, type.getStructMetadata());
130. case MAP:
131. > return new MapThriftCodec<>(type, getElementCodec(type.getKeyTypeReference()), getElementCodec(type.getValueTypeReference()));
132. case SET:
133. return new SetThriftCodec<>(type, getElementCodec(type.getValueTypeReference()));
```

The method cannot return a null value:
```java
public ThriftTypeReference getKeyTypeReference()
{
checkState(keyTypeReference != null, "%s does not have a key", protocolType);
return keyTypeReference;
}
```