Github user actuaryzhang commented on the issue:
https://github.com/apache/spark/pull/16740
The following is a simple example to illustrate the issue.
```
val dataset = Seq(
(1.0, 1.0, 2.0, 0.0, 5.0),
(0.5, 2.0, 1.0, 1.0, 2.0),
(1.0, 3.0, 0.5, 2.0, 1.0),
(2.0, 4.0, 1.5, 3.0, 3.0)
).toDF("y", "w", "off", "x1", "x2")
val formula = new RFormula().setFormula("y ~ 1")
val output = formula.fit(dataset).transform(dataset)
val glr = new GeneralizedLinearRegression().setFamily("poisson")
val model = glr.fit(output)
```
The above prints out the following error message:
```
java.lang.UnsupportedOperationException: empty.reduceLeft
at
scala.collection.TraversableOnce$class.reduceLeft(TraversableOnce.scala:180)
at
scala.collection.mutable.ArrayOps$ofDouble.scala$collection$IndexedSeqOptimized$$super$reduceLeft(ArrayOps.scala:270)
at
scala.collection.IndexedSeqOptimized$class.reduceLeft(IndexedSeqOptimized.scala:74)
```
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