Fix wrong column type for heterogeneus data (#21)

Co-authored-by: Attilio <attilio.dona@telecomitalia.it>

Author: attdona

src/JSONTables.jl

@@ -62,7 +62,7 @@ function jsontable(x::JSON3.Array{JSON3.Object})
                 if !(k in seen)
                     push!(seen, k)
                     push!(names, k)
-                    types[k] = missT(typeof(v))
+                    types[k] = Union{Missing, missT(typeof(v))}
                 end
             end
         end

test/runtests.jl

@@ -81,4 +81,15 @@ ct = Tables.columntable(jt)
 @test isequal(ct.a, [1, missing, 6, 8, 8])
 @test isequal(ct.d, [missing, 5, 7, missing, 11])
 
+new_field_in_last_row = """
+[
+    {"a": 1, "b": 2},
+    {"b": 4, "c": 8}
+]
+"""
+
+jt = JSONTables.jsontable(new_field_in_last_row)
+ct = Tables.columntable(jt)
+@test isequal(ct.c, [missing, 8])
+
 end