Revert "Preserver type of empty datasets"

This reverts commit e7e8fa5.

lib/red_amber/data_frame_variable_operation.rb

@@ -675,12 +675,7 @@ def update_fields_and_arrays(updater)
           raise DataFrameArgumentError, "Data size mismatch (#{data.size} != #{size})"
         end
 
-        if data.is_a?(Vector)
-          a = data.data
-        else
-          a = Arrow::Array.new(data)
-        end
-
+        a = Arrow::Array.new(data.is_a?(Vector) ? data.to_a : data)
         fields[i] = Arrow::Field.new(key, a.value_data_type)
         arrays[i] = Arrow::ChunkedArray.new([a])
       end

test/test_group.rb

@@ -250,7 +250,7 @@ class GroupTest < Test::Unit::TestCase
         Vectors : 3 numeric
         # key       type   level data_preview
         0 :i        uint8      4 [0, 1, 2, nil], 1 nil
-        1 :count    int64      3 [2, 1, 2, 0]
+        1 :count    uint8      3 [2, 1, 2, 0]
         2 :"sum(f)" double     4 [1.1, 2.2, NaN, nil], 1 NaN, 1 nil
       STR
       assert_equal str, @df.group(:i) { [count(:i, :f, :b), sum] }.tdr_str(tally: 0)