return size = 0 in ColumnAnalysis if its unknown

that is if complex agg did not implement inputSizeFn() so
that segment metadata query shows atleast some information.
also instead of COMPLEX, return type of data stored.

docs/content/SegmentMetadataQuery.md

@@ -47,7 +47,7 @@ The format of the result is:
 ```
 
 Dimension columns will have type `STRING`.  
-Metric columns will have type `FLOAT`.  
+Metric columns will have type `FLOAT` or `LONG` or name of the underlying complex type such as `hyperUnique` in case of COMPLEX metric.
 Timestamp column will have type `LONG`.
 
 Only columns which are dimensions (ie, have type `STRING`) will have any cardinality. Rest of the columns (timestamp and metric columns) will show cardinality as `null`.

processing/src/main/java/io/druid/query/metadata/SegmentAnalyzer.java

@@ -143,7 +143,7 @@ public class SegmentAnalyzer
 
     final Function<Object, Long> inputSizeFn = serde.inputSizeFn();
     if (inputSizeFn == null) {
-      return ColumnAnalysis.error("noSizeFn");
+      return new ColumnAnalysis(typeName, 0, null, null);
     }
 
     final int length = column.getLength();
@@ -152,6 +152,6 @@ public class SegmentAnalyzer
       size += inputSizeFn.apply(complexColumn.getRowValue(i));
     }
 
-    return new ColumnAnalysis(capabilities.getType().name(), size, null, null);
+    return new ColumnAnalysis(typeName, size, null, null);
   }
 }