cannot re-use Field in 4.7.2 [LUCENE-5923]

I get an exception "first position increment must be > 0 (got 0) for field ..." when I try to re-use a Field as an entry in a Document. Snippet below.

This works ok on lucene 4.9, but I have to go back to 4.7 for Java 6 compatibility.

Workaround is to not re-use the same object in each Document.

(this is Scala)

private val TypeField = new StringField("TYPE", clazz.getSimpleName, Store.YES)

final def toDocument(t: T): Document = {
val doc = new Document
// Lucene 4.7.2 bug: re-using the common object gives
// "first position increment must be > 0 (got 0) for field 'TYPE'"
//doc.add(TypeField)
doc.add(new StringField("TYPE", clazz.getSimpleName, Store.YES))
doc.add(new StringField("ID", id(t), Store.NO))
doc
}

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Migrated from [LUCENE-5923](https://issues.apache.org/jira/browse/LUCENE-5923) by Sam Halliday

Start with the supplied toDocument reproduction and compare Field reuse behavior between Lucene 4.7.2 and 4.9. Trace the first-position-increment exception from the StringField entry point, then add a regression test demonstrating reuse across Documents and verify the failure is resolved.

Written by the indexing model from the issue text.