Holder instances are returned with null buffer

Creating an instance of holders `new VarCharHolder()` is returning buffer as `null`. What mistake am I making here?

**build.sbt**
```
libraryDependencies ++= Seq(
"org.apache.arrow" % "arrow-vector" % "8.0.0",
"org.apache.arrow" % "arrow-memory-unsafe" % "8.0.0"
)
```

Start with the build.sbt dependencies and the VarCharHolder construction shown in the report; reproduce the null buffer with Arrow 8.0.0. Check the relevant holder API documentation or tests, then document the required setup or confirm whether the reported behavior is expected.

Written by the indexing model from the issue text.