Breaking Change: Added "Missing" support to Field Value Factor (#247)

* bump development version number

* missing support

added missing support to [field value factor](https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-function-score-query.html#function-field-value-factor)

* updated docs

* proposed changes

composer.json

@@ -37,7 +37,7 @@
     "minimum-stability": "dev",
     "extra": {
         "branch-alias": {
-            "dev-master": "5.0-dev"
+            "dev-master": "5.1-dev"
         }
     }
 }

docs/Query/Compound/FunctionScore.md

@@ -105,7 +105,7 @@ $queryArray = $search->toArray();
 ```php
 $functionScoreQuery = new FunctionScoreQuery(new MatchAllQuery());
 $existsQuery = new ExistsQuery('price');
-$functionScoreQuery->addFieldValueFactorFunction('price', 0.5, 'ln', $existsQuery);
+$functionScoreQuery->addFieldValueFactorFunction('price', 0.5, 'ln', $existsQuery, 0);
 
 $search = new Search();
 $search->addQuery($functionScoreQuery);

src/Query/Compound/FunctionScoreQuery.php

@@ -50,18 +50,21 @@ class FunctionScoreQuery implements BuilderInterface
      * @param float            $factor
      * @param string           $modifier
      * @param BuilderInterface $query
-     *
+     * @param mixed            $missing
      * @return $this
      */
-    public function addFieldValueFactorFunction($field, $factor, $modifier = 'none', BuilderInterface $query = null)
+    public function addFieldValueFactorFunction($field, $factor, $modifier = 'none', BuilderInterface $query = null, $missing = null)
     {
-        $function = [
+        $function = array_filter([
             'field_value_factor' => [
                 'field' => $field,
                 'factor' => $factor,
                 'modifier' => $modifier,
+                'missing' => $missing
             ],
-        ];
+        ], function ($item) {
+            return $item !== null;
+        });
 
         $this->applyFilter($function, $query);