Fix issue with duplicate field for WaPo in Solr. (#807)

* Fix issue with duplicate field for WaPo in Solr.

* Add known issues for Solr in v0.6.0

README.md

@@ -98,7 +98,7 @@ See [this page](docs/additional.md) for additional documentation.
 
 ## Release History
 
-+ v0.6.0: September 6, 2019 [[Release Notes](docs/release-notes/release-notes-v0.6.0.md)]
++ v0.6.0: September 6, 2019 [[Release Notes](docs/release-notes/release-notes-v0.6.0.md)][[Known Issues](docs/known-issues/known-issues-v0.6.0.md)]
 + v0.5.1: June 11, 2019 [[Release Notes](docs/release-notes/release-notes-v0.5.1.md)]
 + v0.5.0: June 5, 2019 [[Release Notes](docs/release-notes/release-notes-v0.5.0.md)]
 + v0.4.0: March 4, 2019 [[Release Notes](docs/release-notes/release-notes-v0.4.0.md)]

docs/known-issues/known-issues-v0.6.0.md

@@ -0,0 +1,3 @@
+# Anserini Known Issues (v0.6.0)
+
++ Solr indexing for Washington Post broke due to [417ac12](https://github.com/castorini/anserini/commit/c5ee9af442c500ec43fc28808903cfca2417ac12) and has been fixed in [#807](https://github.com/castorini/anserini/pull/807).

src/main/java/io/anserini/index/IndexCollection.java

@@ -281,6 +281,11 @@ public void run() {
             if (field.fieldType().docValuesType() != DocValuesType.NONE) {
               continue;
             }
+            // If the field is already in the doc, skip it.
+            // This fixes an issue with WaPo where published_date is in the Lucene doc as LongPoint and StoredField. Solr needs one copy, more fine-grained control in config.
+            if (solrDocument.containsKey(field.name())) {
+              continue;
+            }
             if (field.stringValue() != null) { // For some reason, id is multi-valued with null as one of the values
               solrDocument.addField(field.name(), field.stringValue());
             } else if (field.numericValue() != null) {