Aggs: Make it possible to configure missing values.

Most aggregations (terms, histogram, stats, percentiles, geohash-grid) now
support a new `missing` option which defines the value to consider when a
field does not have a value. This can be handy if you eg. want a terms
aggregation to handle the same way documents that have "N/A" or no value
for a `tag` field.

This works in a very similar way to the `missing` option on the `sort`
element.

One known issue is that this option sometimes cannot make the right decision
in the unmapped case: it needs to replace all values with the `missing` value
but might not know what kind of values source should be produced (numerics,
strings, geo points?). For this reason, we might want to add an `unmapped_type`
option in the future like we did for sorting.

Related to #5324

docs/reference/aggregations/bucket/datehistogram-aggregation.asciidoc

@@ -123,3 +123,26 @@ settings and filter the returned buckets based on a `min_doc_count` setting (by
 bucket that matches documents and the last one are returned). This histogram also supports the `extended_bounds`
 setting, which enables extending the bounds of the histogram beyond the data itself (to read more on why you'd want to
 do that please refer to the explanation <<search-aggregations-bucket-histogram-aggregation-extended-bounds,here>>).
+
+==== Missing value
+
+The `missing` parameter defines how documents that are missing a value should be treated.
+By default they will be ignored but it is also possible to treat them as if they
+had a value.
+
+[source,js]
+--------------------------------------------------
+{
+    "aggs" : {
+        "publish_date" : {
+             "datehistogram" : {
+                 "field" : "publish_date",
+                 "interval": "year",
+                 "missing": "2000-01-01" <1>
+             }
+         }
+    }
+}
+--------------------------------------------------
+
+<1> Documents without a value in the `publish_date` field will fall into the same bucket as documents that have the value `2000-01-01`.

docs/reference/aggregations/bucket/histogram-aggregation.asciidoc

@@ -317,3 +317,26 @@ Response:
     }
 }
 --------------------------------------------------
+
+==== Missing value
+
+The `missing` parameter defines how documents that are missing a value should be treated.
+By default they will be ignored but it is also possible to treat them as if they
+had a value.
+
+[source,js]
+--------------------------------------------------
+{
+    "aggs" : {
+        "quantity" : {
+             "histogram" : {
+                 "field" : "quantity",
+                 "interval": 10,
+                 "missing": 0 <1>
+             }
+         }
+    }
+}
+--------------------------------------------------
+
+<1> Documents without a value in the `quantity` field will fall into the same bucket as documents that have the value `0`. 

docs/reference/aggregations/bucket/terms-aggregation.asciidoc

@@ -655,3 +655,25 @@ in inner aggregations.
 <1> experimental[] the possible values are `map`, `global_ordinals`, `global_ordinals_hash` and `global_ordinals_low_cardinality`
 
 Please note that Elasticsearch will ignore this execution hint if it is not applicable and that there is no backward compatibility guarantee on these hints.
+
+==== Missing value
+
+The `missing` parameter defines how documents that are missing a value should be treated.
+By default they will be ignored but it is also possible to treat them as if they
+had a value.
+
+[source,js]
+--------------------------------------------------
+{
+    "aggs" : {
+        "tags" : {
+             "terms" : {
+                 "field" : "tags",
+                 "missing": "N/A" <1>
+             }
+         }
+    }
+}
+--------------------------------------------------
+
+<1> Documents without a value in the `tags` field will fall into the same bucket as documents that have the value `N/A`. 

docs/reference/aggregations/metrics/avg-aggregation.asciidoc

@@ -72,4 +72,26 @@ It turned out that the exam was way above the level of the students and a grade
         }
     }
 }
---------------------------------------------------
+--------------------------------------------------
+
+==== Missing value
+
+The `missing` parameter defines how documents that are missing a value should be treated.
+By default they will be ignored but it is also possible to treat them as if they
+had a value.
+
+[source,js]
+--------------------------------------------------
+{
+    "aggs" : {
+        "grade_avg" : {
+            "avg" : {
+                "field" : "grade",
+                "missing": 10 <1>
+            }
+        }
+    }
+}
+--------------------------------------------------
+
+<1> Documents without a value in the `grade` field will fall into the same bucket as documents that have the value `10`.

docs/reference/aggregations/metrics/cardinality-aggregation.asciidoc

@@ -155,3 +155,24 @@ however since hashes need to be computed on the fly.
 
 TIP: The `script` parameter expects an inline script. Use `script_id` for indexed scripts and `script_file` for scripts in the `config/scripts/` directory.
 
+==== Missing value
+
+The `missing` parameter defines how documents that are missing a value should be treated.
+By default they will be ignored but it is also possible to treat them as if they
+had a value.
+
+[source,js]
+--------------------------------------------------
+{
+    "aggs" : {
+        "tag_cardinality" : {
+            "cardinality" : {
+                "field" : "tag",
+                "missing": "N/A" <1>
+            }
+        }
+    }
+}
+--------------------------------------------------
+
+<1> Documents without a value in the `tag` field will fall into the same bucket as documents that have the value `N/A`.

docs/reference/aggregations/metrics/extendedstats-aggregation.asciidoc

@@ -116,4 +116,26 @@ It turned out that the exam was way above the level of the students and a grade
         }
     }
 }
---------------------------------------------------
+--------------------------------------------------
+
+==== Missing value
+
+The `missing` parameter defines how documents that are missing a value should be treated.
+By default they will be ignored but it is also possible to treat them as if they
+had a value.
+
+[source,js]
+--------------------------------------------------
+{
+    "aggs" : {
+        "grades_stats" : {
+            "extended_stats" : {
+                "field" : "grade",
+                "missing": 0 <1>
+            }
+        }
+    }
+}
+--------------------------------------------------
+
+<1> Documents without a value in the `grade` field will fall into the same bucket as documents that have the value `0`.

docs/reference/aggregations/metrics/max-aggregation.asciidoc

@@ -67,3 +67,24 @@ Let's say that the prices of the documents in our index are in USD, but we would
 }
 --------------------------------------------------
 
+==== Missing value
+
+The `missing` parameter defines how documents that are missing a value should be treated.
+By default they will be ignored but it is also possible to treat them as if they
+had a value.
+
+[source,js]
+--------------------------------------------------
+{
+    "aggs" : {
+        "grade_max" : {
+            "max" : {
+                "field" : "grade",
+                "missing": 10 <1>
+            }
+        }
+    }
+}
+--------------------------------------------------
+
+<1> Documents without a value in the `grade` field will fall into the same bucket as documents that have the value `10`.

docs/reference/aggregations/metrics/min-aggregation.asciidoc

@@ -66,3 +66,25 @@ Let's say that the prices of the documents in our index are in USD, but we would
     }
 }
 --------------------------------------------------
+
+==== Missing value
+
+The `missing` parameter defines how documents that are missing a value should be treated.
+By default they will be ignored but it is also possible to treat them as if they
+had a value.
+
+[source,js]
+--------------------------------------------------
+{
+    "aggs" : {
+        "grade_min" : {
+            "min" : {
+                "field" : "grade",
+                "missing": 10 <1>
+            }
+        }
+    }
+}
+--------------------------------------------------
+
+<1> Documents without a value in the `grade` field will fall into the same bucket as documents that have the value `10`. 

docs/reference/aggregations/metrics/percentile-aggregation.asciidoc

@@ -190,3 +190,25 @@ A "node" uses roughly 32 bytes of memory, so under worst-case scenarios (large a
 of data which arrives sorted and in-order) the default settings will produce a
 TDigest roughly 64KB in size.  In practice data tends to be more random and
 the TDigest will use less memory.
+
+==== Missing value
+
+The `missing` parameter defines how documents that are missing a value should be treated.
+By default they will be ignored but it is also possible to treat them as if they
+had a value.
+
+[source,js]
+--------------------------------------------------
+{
+    "aggs" : {
+        "grade_percentiles" : {
+            "percentiles" : {
+                "field" : "grade",
+                "missing": 10 <1>
+            }
+        }
+    }
+}
+--------------------------------------------------
+
+<1> Documents without a value in the `grade` field will fall into the same bucket as documents that have the value `10`.

docs/reference/aggregations/metrics/percentile-rank-aggregation.asciidoc

@@ -86,3 +86,25 @@ script to generate values which percentile ranks are calculated on
 <2> Scripting supports parameterized input just like any other script
 
 TIP: The `script` parameter expects an inline script. Use `script_id` for indexed scripts and `script_file` for scripts in the `config/scripts/` directory.
+
+==== Missing value
+
+The `missing` parameter defines how documents that are missing a value should be treated.
+By default they will be ignored but it is also possible to treat them as if they
+had a value.
+
+[source,js]
+--------------------------------------------------
+{
+    "aggs" : {
+        "grade_ranks" : {
+            "percentile_ranks" : {
+                "field" : "grade",
+                "missing": 10 <1>
+            }
+        }
+    }
+}
+--------------------------------------------------
+
+<1> Documents without a value in the `grade` field will fall into the same bucket as documents that have the value `10`.

docs/reference/aggregations/metrics/stats-aggregation.asciidoc

@@ -78,4 +78,26 @@ It turned out that the exam was way above the level of the students and a grade
         }
     }
 }
---------------------------------------------------
+--------------------------------------------------
+
+==== Missing value
+
+The `missing` parameter defines how documents that are missing a value should be treated.
+By default they will be ignored but it is also possible to treat them as if they
+had a value.
+
+[source,js]
+--------------------------------------------------
+{
+    "aggs" : {
+        "grades_stats" : {
+            "stats" : {
+                "field" : "grade",
+                "missing": 0 <1>
+            }
+        }
+    }
+}
+--------------------------------------------------
+
+<1> Documents without a value in the `grade` field will fall into the same bucket as documents that have the value `0`.

docs/reference/aggregations/metrics/sum-aggregation.asciidoc

@@ -77,3 +77,25 @@ Computing the sum of squares over all stock tick changes:
     }
 }
 --------------------------------------------------
+
+==== Missing value
+
+The `missing` parameter defines how documents that are missing a value should be treated.
+By default they will be ignored but it is also possible to treat them as if they
+had a value.
+
+[source,js]
+--------------------------------------------------
+{
+    "aggs" : {
+        "total_time" : {
+            "sum" : {
+                "field" : "took",
+                "missing": 100 <1>
+            }
+        }
+    }
+}
+--------------------------------------------------
+
+<1> Documents without a value in the `took` field will fall into the same bucket as documents that have the value `100`.

src/main/java/org/elasticsearch/common/geo/GeoUtils.java

@@ -409,19 +409,24 @@ public static GeoPoint parseGeoPoint(XContentParser parser, GeoPoint point) thro
             return point.reset(lat, lon);
         } else if(parser.currentToken() == Token.VALUE_STRING) {
             String data = parser.text();
-            int comma = data.indexOf(',');
-            if(comma > 0) {
-                lat = Double.parseDouble(data.substring(0, comma).trim());
-                lon = Double.parseDouble(data.substring(comma + 1).trim());
-                return point.reset(lat, lon);
-            } else {
-                return point.resetFromGeoHash(data);
-            }
+            return parseGeoPoint(data, point);
         } else {
             throw new ElasticsearchParseException("geo_point expected");
         }
     }
 
+    /** parse a {@link GeoPoint} from a String */
+    public static GeoPoint parseGeoPoint(String data, GeoPoint point) {
+        int comma = data.indexOf(',');
+        if(comma > 0) {
+            double lat = Double.parseDouble(data.substring(0, comma).trim());
+            double lon = Double.parseDouble(data.substring(comma + 1).trim());
+            return point.reset(lat, lon);
+        } else {
+            return point.resetFromGeoHash(data);
+        }
+    }
+
     private GeoUtils() {
     }
 }

src/main/java/org/elasticsearch/search/aggregations/ValuesSourceAggregationBuilder.java

@@ -34,6 +34,7 @@ public abstract class ValuesSourceAggregationBuilder<B extends ValuesSourceAggre
     private String script;
     private String lang;
     private Map<String, Object> params;
+    private Object missing;
 
     /**
      * Constructs a new builder.
@@ -117,6 +118,14 @@ public B params(Map<String, Object> params) {
         return (B) this;
     }
 
+    /**
+     * Configure the value to use when documents miss a value.
+     */
+    public B missing(Object missingValue) {
+        this.missing = missingValue;
+        return (B) this;
+    }
+
     @Override
     protected final XContentBuilder internalXContent(XContentBuilder builder, Params params) throws IOException {
         builder.startObject();
@@ -132,6 +141,9 @@ protected final XContentBuilder internalXContent(XContentBuilder builder, Params
         if (this.params != null) {
             builder.field("params").map(this.params);
         }
+        if (missing != null) {
+            builder.field("missing", missing);
+        }
 
         doInternalXContent(builder, params);
         return builder.endObject();