diff --git a/github_rest_api/_test.pony b/github_rest_api/_test.pony
index 36d8a66..e20dcaa 100644
--- a/github_rest_api/_test.pony
+++ b/github_rest_api/_test.pony
@@ -23,6 +23,15 @@ actor \nodoc\ Main is TestList
     test(_TestCommitFileJsonConverterMissingField)
     test(_TestGistChangeStatusJsonConverterPreservesValues)
     test(_TestGistChangeStatusJsonConverterMissingField)
+    test(_TestLabelJsonConverterPreservesValues)
+    test(_TestLabelJsonConverterMissingField)
+    test(_TestIssuePRJsonConverterPreservesValues)
+    test(_TestIssuePRJsonConverterMissingField)
+    test(_TestAssetJsonConverterPreservesValues)
+    test(_TestAssetJsonConverterMissingField)
+    test(_TestGistFileJsonConverterPreservesValues)
+    test(_TestGistFileJsonConverterMissingField)
+    test(_TestGistFileJsonConverterAbsentOptionalFields)
     req.QueryParamsTests.make().tests(test)
 
 class \nodoc\ _TestExtractPaginationLinksNoLinks is UnitTest
diff --git a/github_rest_api/_test_json_converters.pony b/github_rest_api/_test_json_converters.pony
index 5313144..ae1c789 100644
--- a/github_rest_api/_test_json_converters.pony
+++ b/github_rest_api/_test_json_converters.pony
@@ -212,3 +212,513 @@ class \nodoc\ _TestGistChangeStatusJsonConverterMissingField is UnitTest
             + skip_idx.string())
         end
       })?
+
+primitive \nodoc\ _TestUserJson
+  """
+  Builds a valid User JSON object for testing converters that nest a User.
+  """
+  fun apply(b: String val): JsonObject =>
+    JsonObject
+      .update("login", "login_" + b)
+      .update("id", I64(1))
+      .update("node_id", "unode_" + b)
+      .update("avatar_url", "avatar_" + b)
+      .update("gravatar_id", "gravatar_" + b)
+      .update("url", "uurl_" + b)
+      .update("html_url", "uhurl_" + b)
+      .update("followers_url", "furl_" + b)
+      .update("following_url", "fourl_" + b)
+      .update("gists_url", "gurl_" + b)
+      .update("starred_url", "surl_" + b)
+      .update("subscriptions_url", "suburl_" + b)
+      .update("organizations_url", "ourl_" + b)
+      .update("repos_url", "rurl_" + b)
+      .update("events_url", "eurl_" + b)
+      .update("received_events_url", "reurl_" + b)
+      .update("type", "User")
+      .update("site_admin", false)
+
+class \nodoc\ _TestLabelJsonConverterPreservesValues is UnitTest
+  fun name(): String => "label-json-converter/preserves-values"
+
+  fun ref apply(h: TestHelper) ? =>
+    PonyCheck.for_all2[String, Bool](
+      recover val Generators.ascii_printable(1, 20) end,
+      recover val Generators.bool() end, h)(
+      {(base, desc_is_null, h) =>
+        let auth = lori.TCPConnectAuth(h.env.root)
+        let creds = req.Credentials(auth)
+        let b: String val = base.clone()
+        let id_val: I64 = 42
+        let node_id_val: String val = "nid_" + b
+        let url_val: String val = "url_" + b
+        let name_val: String val = "name_" + b
+        let color_val: String val = "color_" + b
+        let desc_val: String val = "desc_" + b
+        var obj = JsonObject
+          .update("id", id_val)
+          .update("node_id", node_id_val)
+          .update("url", url_val)
+          .update("name", name_val)
+          .update("color", color_val)
+          .update("default", false)
+        if desc_is_null then
+          obj = obj.update("description", None)
+        else
+          obj = obj.update("description", desc_val)
+        end
+        let json = JsonNav(obj)
+        try
+          let lbl = LabelJsonConverter(json, creds)?
+          h.assert_eq[I64](id_val, lbl.id)
+          h.assert_eq[String](node_id_val, lbl.node_id)
+          h.assert_eq[String](url_val, lbl.url)
+          h.assert_eq[String](name_val, lbl.name)
+          h.assert_eq[String](color_val, lbl.color)
+          h.assert_false(lbl.default, "default should be false")
+          if desc_is_null then
+            match lbl.description
+            | None => None
+            | let _: String =>
+              h.fail("description should be None")
+            end
+          else
+            match lbl.description
+            | let s: String =>
+              h.assert_eq[String](desc_val, s)
+            | None =>
+              h.fail("description should be String")
+            end
+          end
+        else
+          h.fail("converter raised an error")
+        end
+      })?
+
+class \nodoc\ _TestLabelJsonConverterMissingField is UnitTest
+  fun name(): String => "label-json-converter/missing-field"
+
+  fun ref apply(h: TestHelper) ? =>
+    PonyCheck.for_all2[String, USize](
+      recover val Generators.ascii_printable(1, 20) end,
+      recover val Generators.usize(0, 6) end, h)(
+      {(base, skip_idx, h) =>
+        let auth = lori.TCPConnectAuth(h.env.root)
+        let creds = req.Credentials(auth)
+        let b: String val = base.clone()
+        var obj = JsonObject
+        if skip_idx != 0 then obj = obj.update("id", I64(42)) end
+        if skip_idx != 1 then
+          obj = obj.update("node_id", "nid_" + b)
+        end
+        if skip_idx != 2 then
+          obj = obj.update("url", "url_" + b)
+        end
+        if skip_idx != 3 then
+          obj = obj.update("name", "name_" + b)
+        end
+        if skip_idx != 4 then
+          obj = obj.update("color", "color_" + b)
+        end
+        if skip_idx != 5 then obj = obj.update("default", false) end
+        if skip_idx != 6 then
+          obj = obj.update("description", "desc_" + b)
+        end
+        let json = JsonNav(obj)
+        try
+          LabelJsonConverter(json, creds)?
+          h.fail(
+            "converter should have raised for missing "
+              + "field at index " + skip_idx.string())
+        end
+      })?
+
+class \nodoc\ _TestIssuePRJsonConverterPreservesValues is UnitTest
+  fun name(): String =>
+    "issue-pull-request-json-converter/preserves-values"
+
+  fun ref apply(h: TestHelper) ? =>
+    PonyCheck.for_all2[String, Bool](
+      recover val Generators.ascii_printable(1, 20) end,
+      recover val Generators.bool() end, h)(
+      {(base, merged_is_null, h) =>
+        let auth = lori.TCPConnectAuth(h.env.root)
+        let creds = req.Credentials(auth)
+        let b: String val = base.clone()
+        let url_val: String val = "url_" + b
+        let html_url_val: String val = "html_" + b
+        let diff_url_val: String val = "diff_" + b
+        let patch_url_val: String val = "patch_" + b
+        let merged_val: String val = "merged_" + b
+        var obj = JsonObject
+          .update("url", url_val)
+          .update("html_url", html_url_val)
+          .update("diff_url", diff_url_val)
+          .update("patch_url", patch_url_val)
+        if merged_is_null then
+          obj = obj.update("merged_at", None)
+        else
+          obj = obj.update("merged_at", merged_val)
+        end
+        let json = JsonNav(obj)
+        try
+          let ipr =
+            IssuePullRequestJsonConverter(json, creds)?
+          h.assert_eq[String](url_val, ipr.url)
+          h.assert_eq[String](html_url_val, ipr.html_url)
+          h.assert_eq[String](diff_url_val, ipr.diff_url)
+          h.assert_eq[String](patch_url_val, ipr.patch_url)
+          if merged_is_null then
+            match ipr.merged_at
+            | None => None
+            | let _: String =>
+              h.fail("merged_at should be None")
+            end
+          else
+            match ipr.merged_at
+            | let s: String =>
+              h.assert_eq[String](merged_val, s)
+            | None =>
+              h.fail("merged_at should be String")
+            end
+          end
+        else
+          h.fail("converter raised an error")
+        end
+      })?
+
+class \nodoc\ _TestIssuePRJsonConverterMissingField is UnitTest
+  fun name(): String =>
+    "issue-pull-request-json-converter/missing-field"
+
+  fun ref apply(h: TestHelper) ? =>
+    PonyCheck.for_all2[String, USize](
+      recover val Generators.ascii_printable(1, 20) end,
+      recover val Generators.usize(0, 4) end, h)(
+      {(base, skip_idx, h) =>
+        let auth = lori.TCPConnectAuth(h.env.root)
+        let creds = req.Credentials(auth)
+        let b: String val = base.clone()
+        var obj = JsonObject
+        if skip_idx != 0 then
+          obj = obj.update("url", "url_" + b)
+        end
+        if skip_idx != 1 then
+          obj = obj.update("html_url", "html_" + b)
+        end
+        if skip_idx != 2 then
+          obj = obj.update("diff_url", "diff_" + b)
+        end
+        if skip_idx != 3 then
+          obj = obj.update("patch_url", "patch_" + b)
+        end
+        if skip_idx != 4 then
+          obj = obj.update("merged_at", "m_" + b)
+        end
+        let json = JsonNav(obj)
+        try
+          IssuePullRequestJsonConverter(json, creds)?
+          h.fail(
+            "converter should have raised for missing "
+              + "field at index " + skip_idx.string())
+        end
+      })?
+
+class \nodoc\ _TestAssetJsonConverterPreservesValues is UnitTest
+  fun name(): String =>
+    "asset-json-converter/preserves-values"
+
+  fun ref apply(h: TestHelper) ? =>
+    PonyCheck.for_all2[String, Bool](
+      recover val Generators.ascii_printable(1, 20) end,
+      recover val Generators.bool() end, h)(
+      {(base, label_is_null, h) =>
+        let auth = lori.TCPConnectAuth(h.env.root)
+        let creds = req.Credentials(auth)
+        let b: String val = base.clone()
+        let id_val: I64 = 42
+        let node_id_val: String val = "nid_" + b
+        let name_val: String val = "name_" + b
+        let label_val: String val = "label_" + b
+        let ct_val: String val = "ct_" + b
+        let state_val: String val = "state_" + b
+        let size_val: I64 = 1024
+        let dl_val: I64 = 99
+        let ca_val: String val = "ca_" + b
+        let ua_val: String val = "ua_" + b
+        let url_val: String val = "url_" + b
+        let bd_val: String val = "bd_" + b
+        let uploader_obj = _TestUserJson(b)
+        var obj = JsonObject
+          .update("id", id_val)
+          .update("node_id", node_id_val)
+          .update("name", name_val)
+          .update("uploader", uploader_obj)
+          .update("content_type", ct_val)
+          .update("state", state_val)
+          .update("size", size_val)
+          .update("download_count", dl_val)
+          .update("created_at", ca_val)
+          .update("updated_at", ua_val)
+          .update("url", url_val)
+          .update("browser_download_url", bd_val)
+        if label_is_null then
+          obj = obj.update("label", None)
+        else
+          obj = obj.update("label", label_val)
+        end
+        let json = JsonNav(obj)
+        try
+          let asset = AssetJsonConverter(json, creds)?
+          h.assert_eq[I64](id_val, asset.id)
+          h.assert_eq[String](node_id_val, asset.node_id)
+          h.assert_eq[String](name_val, asset.name)
+          h.assert_eq[String](ct_val, asset.content_type)
+          h.assert_eq[String](state_val, asset.state)
+          h.assert_eq[I64](size_val, asset.size)
+          h.assert_eq[I64](dl_val, asset.download_count)
+          h.assert_eq[String](ca_val, asset.created_at)
+          h.assert_eq[String](ua_val, asset.updated_at)
+          h.assert_eq[String](url_val, asset.url)
+          h.assert_eq[String](bd_val,
+            asset.browser_download_url)
+          h.assert_eq[String]("login_" + b,
+            asset.uploader.login)
+          h.assert_eq[I64](I64(1), asset.uploader.id)
+          if label_is_null then
+            match asset.label
+            | None => None
+            | let _: String =>
+              h.fail("label should be None")
+            end
+          else
+            match asset.label
+            | let s: String =>
+              h.assert_eq[String](label_val, s)
+            | None =>
+              h.fail("label should be String")
+            end
+          end
+        else
+          h.fail("converter raised an error")
+        end
+      })?
+
+class \nodoc\ _TestAssetJsonConverterMissingField is UnitTest
+  fun name(): String =>
+    "asset-json-converter/missing-field"
+
+  fun ref apply(h: TestHelper) ? =>
+    PonyCheck.for_all2[String, USize](
+      recover val Generators.ascii_printable(1, 20) end,
+      recover val Generators.usize(0, 12) end, h)(
+      {(base, skip_idx, h) =>
+        let auth = lori.TCPConnectAuth(h.env.root)
+        let creds = req.Credentials(auth)
+        let b: String val = base.clone()
+        let uploader_obj = _TestUserJson(b)
+        var obj = JsonObject
+        if skip_idx != 0 then
+          obj = obj.update("id", I64(42))
+        end
+        if skip_idx != 1 then
+          obj = obj.update("node_id", "nid_" + b)
+        end
+        if skip_idx != 2 then
+          obj = obj.update("name", "name_" + b)
+        end
+        if skip_idx != 3 then
+          obj = obj.update("label", "lbl_" + b)
+        end
+        if skip_idx != 4 then
+          obj = obj.update("uploader", uploader_obj)
+        end
+        if skip_idx != 5 then
+          obj = obj.update("content_type", "ct_" + b)
+        end
+        if skip_idx != 6 then
+          obj = obj.update("state", "st_" + b)
+        end
+        if skip_idx != 7 then
+          obj = obj.update("size", I64(100))
+        end
+        if skip_idx != 8 then
+          obj = obj.update("download_count", I64(50))
+        end
+        if skip_idx != 9 then
+          obj = obj.update("created_at", "ca_" + b)
+        end
+        if skip_idx != 10 then
+          obj = obj.update("updated_at", "ua_" + b)
+        end
+        if skip_idx != 11 then
+          obj = obj.update("url", "url_" + b)
+        end
+        if skip_idx != 12 then
+          obj = obj.update(
+            "browser_download_url", "bd_" + b)
+        end
+        let json = JsonNav(obj)
+        try
+          AssetJsonConverter(json, creds)?
+          h.fail(
+            "converter should have raised for missing "
+              + "field at index " + skip_idx.string())
+        end
+      })?
+
+class \nodoc\ _TestGistFileJsonConverterPreservesValues is UnitTest
+  fun name(): String =>
+    "gist-file-json-converter/preserves-values"
+
+  fun ref apply(h: TestHelper) ? =>
+    PonyCheck.for_all2[String, Bool](
+      recover val Generators.ascii_printable(1, 20) end,
+      recover val Generators.bool() end, h)(
+      {(base, lang_is_null, h) =>
+        let auth = lori.TCPConnectAuth(h.env.root)
+        let creds = req.Credentials(auth)
+        let b: String val = base.clone()
+        let fn_val: String val = "fn_" + b
+        let ct_val: String val = "ct_" + b
+        let lang_val: String val = "lang_" + b
+        let raw_val: String val = "raw_" + b
+        let size_val: I64 = 256
+        let content_val: String val = "content_" + b
+        let encoding_val: String val = "utf-8"
+        var obj = JsonObject
+          .update("filename", fn_val)
+          .update("type", ct_val)
+          .update("raw_url", raw_val)
+          .update("size", size_val)
+          .update("content", content_val)
+          .update("encoding", encoding_val)
+          .update("truncated", false)
+        if lang_is_null then
+          obj = obj.update("language", None)
+        else
+          obj = obj.update("language", lang_val)
+        end
+        let json = JsonNav(obj)
+        try
+          let gf = GistFileJsonConverter(json, creds)?
+          h.assert_eq[String](fn_val, gf.filename)
+          h.assert_eq[String](ct_val, gf.content_type)
+          h.assert_eq[String](raw_val, gf.raw_url)
+          h.assert_eq[I64](size_val, gf.size)
+          match gf.content
+          | let s: String =>
+            h.assert_eq[String](content_val, s)
+          | None =>
+            h.fail("content should be String")
+          end
+          match gf.encoding
+          | let s: String =>
+            h.assert_eq[String](encoding_val, s)
+          | None =>
+            h.fail("encoding should be String")
+          end
+          match gf.truncated
+          | let t: Bool =>
+            h.assert_false(t, "truncated should be false")
+          | None =>
+            h.fail("truncated should be Bool")
+          end
+          if lang_is_null then
+            match gf.language
+            | None => None
+            | let _: String =>
+              h.fail("language should be None")
+            end
+          else
+            match gf.language
+            | let s: String =>
+              h.assert_eq[String](lang_val, s)
+            | None =>
+              h.fail("language should be String")
+            end
+          end
+        else
+          h.fail("converter raised an error")
+        end
+      })?
+
+class \nodoc\ _TestGistFileJsonConverterMissingField is UnitTest
+  fun name(): String =>
+    "gist-file-json-converter/missing-field"
+
+  fun ref apply(h: TestHelper) ? =>
+    PonyCheck.for_all2[String, USize](
+      recover val Generators.ascii_printable(1, 20) end,
+      recover val Generators.usize(0, 4) end, h)(
+      {(base, skip_idx, h) =>
+        let auth = lori.TCPConnectAuth(h.env.root)
+        let creds = req.Credentials(auth)
+        let b: String val = base.clone()
+        var obj = JsonObject
+        if skip_idx != 0 then
+          obj = obj.update("filename", "fn_" + b)
+        end
+        if skip_idx != 1 then
+          obj = obj.update("type", "ct_" + b)
+        end
+        if skip_idx != 2 then
+          obj = obj.update("language", "lang_" + b)
+        end
+        if skip_idx != 3 then
+          obj = obj.update("raw_url", "raw_" + b)
+        end
+        if skip_idx != 4 then
+          obj = obj.update("size", I64(100))
+        end
+        let json = JsonNav(obj)
+        try
+          GistFileJsonConverter(json, creds)?
+          h.fail(
+            "converter should have raised for missing "
+              + "field at index " + skip_idx.string())
+        end
+      })?
+
+class \nodoc\ _TestGistFileJsonConverterAbsentOptionalFields is UnitTest
+  fun name(): String =>
+    "gist-file-json-converter/absent-optional-fields"
+
+  fun ref apply(h: TestHelper) ? =>
+    PonyCheck.for_all[String](
+      recover val Generators.ascii_printable(1, 20) end, h)(
+      {(base, h) =>
+        let auth = lori.TCPConnectAuth(h.env.root)
+        let creds = req.Credentials(auth)
+        let b: String val = base.clone()
+        let obj = JsonObject
+          .update("filename", "fn_" + b)
+          .update("type", "ct_" + b)
+          .update("language", "lang_" + b)
+          .update("raw_url", "raw_" + b)
+          .update("size", I64(100))
+        let json = JsonNav(obj)
+        try
+          let gf = GistFileJsonConverter(json, creds)?
+          h.assert_eq[String]("fn_" + b, gf.filename)
+          h.assert_eq[String]("ct_" + b, gf.content_type)
+          h.assert_eq[I64](I64(100), gf.size)
+          match gf.content
+          | None => None
+          | let _: String =>
+            h.fail("content should be None")
+          end
+          match gf.encoding
+          | None => None
+          | let _: String =>
+            h.fail("encoding should be None")
+          end
+          match gf.truncated
+          | None => None
+          | let _: Bool =>
+            h.fail("truncated should be None")
+          end
+        else
+          h.fail("converter raised an error")
+        end
+      })?