max_score == NaN, closes #263.

.idea/dictionaries/kimchy.xml

@@ -2,10 +2,12 @@
   <dictionary name="kimchy">
     <words>
       <w>addr</w>
+      <w>amazonaws</w>
       <w>appendable</w>
       <w>args</w>
       <w>asciifolding</w>
       <w>attr</w>
+      <w>auth</w>
       <w>banon</w>
       <w>bindhost</w>
       <w>birthdate</w>

modules/elasticsearch/src/main/java/org/elasticsearch/search/internal/InternalSearchHits.java

@@ -98,7 +98,11 @@ public class InternalSearchHits implements SearchHits {
     @Override public void toXContent(XContentBuilder builder, Params params) throws IOException {
         builder.startObject("hits");
         builder.field("total", totalHits);
+        if (Float.isNaN(maxScore)) {
+            builder.nullField("max_score");
+        } else {
             builder.field("max_score", maxScore);
+        }
         builder.field("hits");
         builder.startArray();
         for (SearchHit hit : hits) {