diff --git a/.travis.yml b/.travis.yml
index 1e22143c7..b1c4a9cae 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -37,9 +37,9 @@ before_install:
 
 install:
   - travis_retry gem install bundler
-  - travis_retry nvm install 9.11.1
+  - travis_retry nvm install 8.11.3
   - node -v
-  - travis_retry npm i -g yarn@0.27.5
+  - travis_retry npm i -g yarn
   - travis_retry yarn global add babel-cli
   - travis_retry bundle install
   - travis_retry yarn
diff --git a/lib/react_on_rails/react_on_rails_helper.rb b/lib/react_on_rails/react_on_rails_helper.rb
index 37e2279b3..765ab6703 100644
--- a/lib/react_on_rails/react_on_rails_helper.rb
+++ b/lib/react_on_rails/react_on_rails_helper.rb
@@ -264,7 +264,7 @@ def server_render_js(js_expression, options = {})
 
     def json_safe_and_pretty(hash_or_string)
       return "{}" if hash_or_string.nil?
-      unless hash_or_string.class.in?([Hash, String])
+      unless hash_or_string.is_a?(String) || hash_or_string.is_a?(Hash)
         raise ReactOnRails::Error, "#{__method__} only accepts String or Hash as argument "\
             "(#{hash_or_string.class} given)."
       end
diff --git a/spec/dummy/Gemfile.lock b/spec/dummy/Gemfile.lock
index c8ad4673f..e6e1af831 100644
--- a/spec/dummy/Gemfile.lock
+++ b/spec/dummy/Gemfile.lock
@@ -7,7 +7,7 @@ GIT
 PATH
   remote: ../..
   specs:
-    react_on_rails (11.0.6)
+    react_on_rails (11.0.7)
       addressable
       connection_pool
       execjs (~> 2.5)
@@ -350,4 +350,4 @@ DEPENDENCIES
   webpacker
 
 BUNDLED WITH
-   1.16.1
+   1.16.2
diff --git a/spec/dummy/spec/helpers/react_on_rails_helper_spec.rb b/spec/dummy/spec/helpers/react_on_rails_helper_spec.rb
index 59743c999..7f3345030 100644
--- a/spec/dummy/spec/helpers/react_on_rails_helper_spec.rb
+++ b/spec/dummy/spec/helpers/react_on_rails_helper_spec.rb
@@ -35,6 +35,16 @@
       expect { helper.json_safe_and_pretty(false) }.to raise_error
     end
 
+    it "should return empty json when an empty Hash" do
+      escaped_json = helper.json_safe_and_pretty({})
+      expect(escaped_json).to eq("{}")
+    end
+
+    it "should return empty json when an empty HashWithIndifferentAccess" do
+      escaped_json = helper.json_safe_and_pretty(HashWithIndifferentAccess.new)
+      expect(escaped_json).to eq("{}")
+    end
+
     it "should return empty json when nil" do
       escaped_json = helper.json_safe_and_pretty(nil)
       expect(escaped_json).to eq("{}")
diff --git a/spec/dummy/yarn.lock b/spec/dummy/yarn.lock
index fb57ccd13..0eda22335 100644
--- a/spec/dummy/yarn.lock
+++ b/spec/dummy/yarn.lock
@@ -2,3 +2,406 @@
 # yarn lockfile v1
 
 
+abbrev@1:
+  version "1.1.1"
+  resolved "https://registry.yarnpkg.com/abbrev/-/abbrev-1.1.1.tgz#f8f2c887ad10bf67f634f005b6987fed3179aac8"
+
+ansi-regex@^2.0.0:
+  version "2.1.1"
+  resolved "https://registry.yarnpkg.com/ansi-regex/-/ansi-regex-2.1.1.tgz#c3b33ab5ee360d86e0e628f0468ae7ef27d654df"
+
+ansi-regex@^3.0.0:
+  version "3.0.0"
+  resolved "https://registry.yarnpkg.com/ansi-regex/-/ansi-regex-3.0.0.tgz#ed0317c322064f79466c02966bddb605ab37d998"
+
+aproba@^1.0.3:
+  version "1.2.0"
+  resolved "https://registry.yarnpkg.com/aproba/-/aproba-1.2.0.tgz#6802e6264efd18c790a1b0d517f0f2627bf2c94a"
+
+are-we-there-yet@~1.1.2:
+  version "1.1.5"
+  resolved "https://registry.yarnpkg.com/are-we-there-yet/-/are-we-there-yet-1.1.5.tgz#4b35c2944f062a8bfcda66410760350fe9ddfc21"
+  dependencies:
+    delegates "^1.0.0"
+    readable-stream "^2.0.6"
+
+balanced-match@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/balanced-match/-/balanced-match-1.0.0.tgz#89b4d199ab2bee49de164ea02b89ce462d71b767"
+
+brace-expansion@^1.1.7:
+  version "1.1.11"
+  resolved "https://registry.yarnpkg.com/brace-expansion/-/brace-expansion-1.1.11.tgz#3c7fcbf529d87226f3d2f52b966ff5271eb441dd"
+  dependencies:
+    balanced-match "^1.0.0"
+    concat-map "0.0.1"
+
+chownr@^1.0.1:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/chownr/-/chownr-1.0.1.tgz#e2a75042a9551908bebd25b8523d5f9769d79181"
+
+code-point-at@^1.0.0:
+  version "1.1.0"
+  resolved "https://registry.yarnpkg.com/code-point-at/-/code-point-at-1.1.0.tgz#0d070b4d043a5bea33a2f1a40e2edb3d9a4ccf77"
+
+concat-map@0.0.1:
+  version "0.0.1"
+  resolved "https://registry.yarnpkg.com/concat-map/-/concat-map-0.0.1.tgz#d8a96bd77fd68df7793a73036a3ba0d5405d477b"
+
+console-control-strings@^1.0.0, console-control-strings@~1.1.0:
+  version "1.1.0"
+  resolved "https://registry.yarnpkg.com/console-control-strings/-/console-control-strings-1.1.0.tgz#3d7cf4464db6446ea644bf4b39507f9851008e8e"
+
+core-util-is@~1.0.0:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/core-util-is/-/core-util-is-1.0.2.tgz#b5fd54220aa2bc5ab57aab7140c940754503c1a7"
+
+debug@^2.1.2:
+  version "2.6.9"
+  resolved "https://registry.yarnpkg.com/debug/-/debug-2.6.9.tgz#5d128515df134ff327e90a4c93f4e077a536341f"
+  dependencies:
+    ms "2.0.0"
+
+deep-extend@^0.6.0:
+  version "0.6.0"
+  resolved "https://registry.yarnpkg.com/deep-extend/-/deep-extend-0.6.0.tgz#c4fa7c95404a17a9c3e8ca7e1537312b736330ac"
+
+delegates@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/delegates/-/delegates-1.0.0.tgz#84c6e159b81904fdca59a0ef44cd870d31250f9a"
+
+detect-libc@^1.0.2:
+  version "1.0.3"
+  resolved "https://registry.yarnpkg.com/detect-libc/-/detect-libc-1.0.3.tgz#fa137c4bd698edf55cd5cd02ac559f91a4c4ba9b"
+
+fs-minipass@^1.2.5:
+  version "1.2.5"
+  resolved "https://registry.yarnpkg.com/fs-minipass/-/fs-minipass-1.2.5.tgz#06c277218454ec288df77ada54a03b8702aacb9d"
+  dependencies:
+    minipass "^2.2.1"
+
+fs.realpath@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/fs.realpath/-/fs.realpath-1.0.0.tgz#1504ad2523158caa40db4a2787cb01411994ea4f"
+
+fsevents@^1.2.4:
+  version "1.2.4"
+  resolved "https://registry.yarnpkg.com/fsevents/-/fsevents-1.2.4.tgz#f41dcb1af2582af3692da36fc55cbd8e1041c426"
+  dependencies:
+    nan "^2.9.2"
+    node-pre-gyp "^0.10.0"
+
+gauge@~2.7.3:
+  version "2.7.4"
+  resolved "https://registry.yarnpkg.com/gauge/-/gauge-2.7.4.tgz#2c03405c7538c39d7eb37b317022e325fb018bf7"
+  dependencies:
+    aproba "^1.0.3"
+    console-control-strings "^1.0.0"
+    has-unicode "^2.0.0"
+    object-assign "^4.1.0"
+    signal-exit "^3.0.0"
+    string-width "^1.0.1"
+    strip-ansi "^3.0.1"
+    wide-align "^1.1.0"
+
+glob@^7.0.5:
+  version "7.1.2"
+  resolved "https://registry.yarnpkg.com/glob/-/glob-7.1.2.tgz#c19c9df9a028702d678612384a6552404c636d15"
+  dependencies:
+    fs.realpath "^1.0.0"
+    inflight "^1.0.4"
+    inherits "2"
+    minimatch "^3.0.4"
+    once "^1.3.0"
+    path-is-absolute "^1.0.0"
+
+has-unicode@^2.0.0:
+  version "2.0.1"
+  resolved "https://registry.yarnpkg.com/has-unicode/-/has-unicode-2.0.1.tgz#e0e6fe6a28cf51138855e086d1691e771de2a8b9"
+
+iconv-lite@^0.4.4:
+  version "0.4.23"
+  resolved "https://registry.yarnpkg.com/iconv-lite/-/iconv-lite-0.4.23.tgz#297871f63be507adcfbfca715d0cd0eed84e9a63"
+  dependencies:
+    safer-buffer ">= 2.1.2 < 3"
+
+ignore-walk@^3.0.1:
+  version "3.0.1"
+  resolved "https://registry.yarnpkg.com/ignore-walk/-/ignore-walk-3.0.1.tgz#a83e62e7d272ac0e3b551aaa82831a19b69f82f8"
+  dependencies:
+    minimatch "^3.0.4"
+
+inflight@^1.0.4:
+  version "1.0.6"
+  resolved "https://registry.yarnpkg.com/inflight/-/inflight-1.0.6.tgz#49bd6331d7d02d0c09bc910a1075ba8165b56df9"
+  dependencies:
+    once "^1.3.0"
+    wrappy "1"
+
+inherits@2, inherits@~2.0.3:
+  version "2.0.3"
+  resolved "https://registry.yarnpkg.com/inherits/-/inherits-2.0.3.tgz#633c2c83e3da42a502f52466022480f4208261de"
+
+ini@~1.3.0:
+  version "1.3.5"
+  resolved "https://registry.yarnpkg.com/ini/-/ini-1.3.5.tgz#eee25f56db1c9ec6085e0c22778083f596abf927"
+
+is-fullwidth-code-point@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/is-fullwidth-code-point/-/is-fullwidth-code-point-1.0.0.tgz#ef9e31386f031a7f0d643af82fde50c457ef00cb"
+  dependencies:
+    number-is-nan "^1.0.0"
+
+is-fullwidth-code-point@^2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/is-fullwidth-code-point/-/is-fullwidth-code-point-2.0.0.tgz#a3b30a5c4f199183167aaab93beefae3ddfb654f"
+
+isarray@~1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/isarray/-/isarray-1.0.0.tgz#bb935d48582cba168c06834957a54a3e07124f11"
+
+minimatch@^3.0.4:
+  version "3.0.4"
+  resolved "https://registry.yarnpkg.com/minimatch/-/minimatch-3.0.4.tgz#5166e286457f03306064be5497e8dbb0c3d32083"
+  dependencies:
+    brace-expansion "^1.1.7"
+
+minimist@0.0.8:
+  version "0.0.8"
+  resolved "https://registry.yarnpkg.com/minimist/-/minimist-0.0.8.tgz#857fcabfc3397d2625b8228262e86aa7a011b05d"
+
+minimist@^1.2.0:
+  version "1.2.0"
+  resolved "https://registry.yarnpkg.com/minimist/-/minimist-1.2.0.tgz#a35008b20f41383eec1fb914f4cd5df79a264284"
+
+minipass@^2.2.1, minipass@^2.3.3:
+  version "2.3.3"
+  resolved "https://registry.yarnpkg.com/minipass/-/minipass-2.3.3.tgz#a7dcc8b7b833f5d368759cce544dccb55f50f233"
+  dependencies:
+    safe-buffer "^5.1.2"
+    yallist "^3.0.0"
+
+minizlib@^1.1.0:
+  version "1.1.0"
+  resolved "https://registry.yarnpkg.com/minizlib/-/minizlib-1.1.0.tgz#11e13658ce46bc3a70a267aac58359d1e0c29ceb"
+  dependencies:
+    minipass "^2.2.1"
+
+mkdirp@^0.5.0, mkdirp@^0.5.1:
+  version "0.5.1"
+  resolved "https://registry.yarnpkg.com/mkdirp/-/mkdirp-0.5.1.tgz#30057438eac6cf7f8c4767f38648d6697d75c903"
+  dependencies:
+    minimist "0.0.8"
+
+ms@2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/ms/-/ms-2.0.0.tgz#5608aeadfc00be6c2901df5f9861788de0d597c8"
+
+nan@^2.9.2:
+  version "2.10.0"
+  resolved "https://registry.yarnpkg.com/nan/-/nan-2.10.0.tgz#96d0cd610ebd58d4b4de9cc0c6828cda99c7548f"
+
+needle@^2.2.0:
+  version "2.2.1"
+  resolved "https://registry.yarnpkg.com/needle/-/needle-2.2.1.tgz#b5e325bd3aae8c2678902fa296f729455d1d3a7d"
+  dependencies:
+    debug "^2.1.2"
+    iconv-lite "^0.4.4"
+    sax "^1.2.4"
+
+node-pre-gyp@^0.10.0:
+  version "0.10.0"
+  resolved "https://registry.yarnpkg.com/node-pre-gyp/-/node-pre-gyp-0.10.0.tgz#6e4ef5bb5c5203c6552448828c852c40111aac46"
+  dependencies:
+    detect-libc "^1.0.2"
+    mkdirp "^0.5.1"
+    needle "^2.2.0"
+    nopt "^4.0.1"
+    npm-packlist "^1.1.6"
+    npmlog "^4.0.2"
+    rc "^1.1.7"
+    rimraf "^2.6.1"
+    semver "^5.3.0"
+    tar "^4"
+
+nopt@^4.0.1:
+  version "4.0.1"
+  resolved "https://registry.yarnpkg.com/nopt/-/nopt-4.0.1.tgz#d0d4685afd5415193c8c7505602d0d17cd64474d"
+  dependencies:
+    abbrev "1"
+    osenv "^0.1.4"
+
+npm-bundled@^1.0.1:
+  version "1.0.3"
+  resolved "https://registry.yarnpkg.com/npm-bundled/-/npm-bundled-1.0.3.tgz#7e71703d973af3370a9591bafe3a63aca0be2308"
+
+npm-packlist@^1.1.6:
+  version "1.1.10"
+  resolved "https://registry.yarnpkg.com/npm-packlist/-/npm-packlist-1.1.10.tgz#1039db9e985727e464df066f4cf0ab6ef85c398a"
+  dependencies:
+    ignore-walk "^3.0.1"
+    npm-bundled "^1.0.1"
+
+npmlog@^4.0.2:
+  version "4.1.2"
+  resolved "https://registry.yarnpkg.com/npmlog/-/npmlog-4.1.2.tgz#08a7f2a8bf734604779a9efa4ad5cc717abb954b"
+  dependencies:
+    are-we-there-yet "~1.1.2"
+    console-control-strings "~1.1.0"
+    gauge "~2.7.3"
+    set-blocking "~2.0.0"
+
+number-is-nan@^1.0.0:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/number-is-nan/-/number-is-nan-1.0.1.tgz#097b602b53422a522c1afb8790318336941a011d"
+
+object-assign@^4.1.0:
+  version "4.1.1"
+  resolved "https://registry.yarnpkg.com/object-assign/-/object-assign-4.1.1.tgz#2109adc7965887cfc05cbbd442cac8bfbb360863"
+
+once@^1.3.0:
+  version "1.4.0"
+  resolved "https://registry.yarnpkg.com/once/-/once-1.4.0.tgz#583b1aa775961d4b113ac17d9c50baef9dd76bd1"
+  dependencies:
+    wrappy "1"
+
+os-homedir@^1.0.0:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/os-homedir/-/os-homedir-1.0.2.tgz#ffbc4988336e0e833de0c168c7ef152121aa7fb3"
+
+os-tmpdir@^1.0.0:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/os-tmpdir/-/os-tmpdir-1.0.2.tgz#bbe67406c79aa85c5cfec766fe5734555dfa1274"
+
+osenv@^0.1.4:
+  version "0.1.5"
+  resolved "https://registry.yarnpkg.com/osenv/-/osenv-0.1.5.tgz#85cdfafaeb28e8677f416e287592b5f3f49ea410"
+  dependencies:
+    os-homedir "^1.0.0"
+    os-tmpdir "^1.0.0"
+
+path-is-absolute@^1.0.0:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/path-is-absolute/-/path-is-absolute-1.0.1.tgz#174b9268735534ffbc7ace6bf53a5a9e1b5c5f5f"
+
+process-nextick-args@~2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/process-nextick-args/-/process-nextick-args-2.0.0.tgz#a37d732f4271b4ab1ad070d35508e8290788ffaa"
+
+rc@^1.1.7:
+  version "1.2.8"
+  resolved "https://registry.yarnpkg.com/rc/-/rc-1.2.8.tgz#cd924bf5200a075b83c188cd6b9e211b7fc0d3ed"
+  dependencies:
+    deep-extend "^0.6.0"
+    ini "~1.3.0"
+    minimist "^1.2.0"
+    strip-json-comments "~2.0.1"
+
+readable-stream@^2.0.6:
+  version "2.3.6"
+  resolved "https://registry.yarnpkg.com/readable-stream/-/readable-stream-2.3.6.tgz#b11c27d88b8ff1fbe070643cf94b0c79ae1b0aaf"
+  dependencies:
+    core-util-is "~1.0.0"
+    inherits "~2.0.3"
+    isarray "~1.0.0"
+    process-nextick-args "~2.0.0"
+    safe-buffer "~5.1.1"
+    string_decoder "~1.1.1"
+    util-deprecate "~1.0.1"
+
+rimraf@^2.6.1:
+  version "2.6.2"
+  resolved "https://registry.yarnpkg.com/rimraf/-/rimraf-2.6.2.tgz#2ed8150d24a16ea8651e6d6ef0f47c4158ce7a36"
+  dependencies:
+    glob "^7.0.5"
+
+safe-buffer@^5.1.2, safe-buffer@~5.1.0, safe-buffer@~5.1.1:
+  version "5.1.2"
+  resolved "https://registry.yarnpkg.com/safe-buffer/-/safe-buffer-5.1.2.tgz#991ec69d296e0313747d59bdfd2b745c35f8828d"
+
+"safer-buffer@>= 2.1.2 < 3":
+  version "2.1.2"
+  resolved "https://registry.yarnpkg.com/safer-buffer/-/safer-buffer-2.1.2.tgz#44fa161b0187b9549dd84bb91802f9bd8385cd6a"
+
+sax@^1.2.4:
+  version "1.2.4"
+  resolved "https://registry.yarnpkg.com/sax/-/sax-1.2.4.tgz#2816234e2378bddc4e5354fab5caa895df7100d9"
+
+semver@^5.3.0:
+  version "5.5.0"
+  resolved "https://registry.yarnpkg.com/semver/-/semver-5.5.0.tgz#dc4bbc7a6ca9d916dee5d43516f0092b58f7b8ab"
+
+set-blocking@~2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/set-blocking/-/set-blocking-2.0.0.tgz#045f9782d011ae9a6803ddd382b24392b3d890f7"
+
+signal-exit@^3.0.0:
+  version "3.0.2"
+  resolved "https://registry.yarnpkg.com/signal-exit/-/signal-exit-3.0.2.tgz#b5fdc08f1287ea1178628e415e25132b73646c6d"
+
+string-width@^1.0.1:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/string-width/-/string-width-1.0.2.tgz#118bdf5b8cdc51a2a7e70d211e07e2b0b9b107d3"
+  dependencies:
+    code-point-at "^1.0.0"
+    is-fullwidth-code-point "^1.0.0"
+    strip-ansi "^3.0.0"
+
+"string-width@^1.0.2 || 2":
+  version "2.1.1"
+  resolved "https://registry.yarnpkg.com/string-width/-/string-width-2.1.1.tgz#ab93f27a8dc13d28cac815c462143a6d9012ae9e"
+  dependencies:
+    is-fullwidth-code-point "^2.0.0"
+    strip-ansi "^4.0.0"
+
+string_decoder@~1.1.1:
+  version "1.1.1"
+  resolved "https://registry.yarnpkg.com/string_decoder/-/string_decoder-1.1.1.tgz#9cf1611ba62685d7030ae9e4ba34149c3af03fc8"
+  dependencies:
+    safe-buffer "~5.1.0"
+
+strip-ansi@^3.0.0, strip-ansi@^3.0.1:
+  version "3.0.1"
+  resolved "https://registry.yarnpkg.com/strip-ansi/-/strip-ansi-3.0.1.tgz#6a385fb8853d952d5ff05d0e8aaf94278dc63dcf"
+  dependencies:
+    ansi-regex "^2.0.0"
+
+strip-ansi@^4.0.0:
+  version "4.0.0"
+  resolved "https://registry.yarnpkg.com/strip-ansi/-/strip-ansi-4.0.0.tgz#a8479022eb1ac368a871389b635262c505ee368f"
+  dependencies:
+    ansi-regex "^3.0.0"
+
+strip-json-comments@~2.0.1:
+  version "2.0.1"
+  resolved "https://registry.yarnpkg.com/strip-json-comments/-/strip-json-comments-2.0.1.tgz#3c531942e908c2697c0ec344858c286c7ca0a60a"
+
+tar@^4:
+  version "4.4.4"
+  resolved "https://registry.yarnpkg.com/tar/-/tar-4.4.4.tgz#ec8409fae9f665a4355cc3b4087d0820232bb8cd"
+  dependencies:
+    chownr "^1.0.1"
+    fs-minipass "^1.2.5"
+    minipass "^2.3.3"
+    minizlib "^1.1.0"
+    mkdirp "^0.5.0"
+    safe-buffer "^5.1.2"
+    yallist "^3.0.2"
+
+util-deprecate@~1.0.1:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/util-deprecate/-/util-deprecate-1.0.2.tgz#450d4dc9fa70de732762fbd2d4a28981419a0ccf"
+
+wide-align@^1.1.0:
+  version "1.1.3"
+  resolved "https://registry.yarnpkg.com/wide-align/-/wide-align-1.1.3.tgz#ae074e6bdc0c14a431e804e624549c633b000457"
+  dependencies:
+    string-width "^1.0.2 || 2"
+
+wrappy@1:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/wrappy/-/wrappy-1.0.2.tgz#b5243d8f3ec1aa35f1364605bc0d1036e30ab69f"
+
+yallist@^3.0.0, yallist@^3.0.2:
+  version "3.0.2"
+  resolved "https://registry.yarnpkg.com/yallist/-/yallist-3.0.2.tgz#8452b4bb7e83c7c188d8041c1a837c773d6d8bb9"