diff --git a/.github/CONTRIBUTING.md b/.github/CONTRIBUTING.md
new file mode 100644
index 0000000..e5ca37b
--- /dev/null
+++ b/.github/CONTRIBUTING.md
@@ -0,0 +1,34 @@
+# CONTRIBUTING
+
+## Code Contributions
+
+## Installation
+
+Install project dependencies and test tools by running the following commands.
+
+```bash
+$ composer install
+```
+
+## Running tests
+
+```bash
+$ composer test
+```
+```bash
+$ composer coverage // xdebug
+$ composer pcov     // pcov
+```
+
+Add tests for your new code ensuring that you have 100% code coverage.
+In rare cases, code may be excluded from test coverage using `@codeCoverageIgnore`.
+
+## Sending a pull request
+
+To ensure your PHP code changes pass the CI checks, make sure to run all the same checks before submitting a PR.
+
+```bash
+$ composer tests
+```
+
+When you make a pull request, the tests will automatically be run again by GH action on multiple php versions.
diff --git a/.github/ISSUE_TEMPLATE/bug_report.md b/.github/ISSUE_TEMPLATE/bug_report.md
new file mode 100644
index 0000000..55e8c3e
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/bug_report.md
@@ -0,0 +1,14 @@
+---
+name: Bug Report
+about: Create a bug report
+labels: Bug
+---
+
+### Bug Report
+
+<!-- Provide a summary describing the problem you are experiencing. -->
+
+### How to reproduce
+
+<!--- Describe exactly how to reproduce the problem, using a minimal test-case or working code sample. -->
+
diff --git a/.github/ISSUE_TEMPLATE/feature.md b/.github/ISSUE_TEMPLATE/feature.md
new file mode 100644
index 0000000..5a19855
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/feature.md
@@ -0,0 +1,7 @@
+---
+name: Feature
+about: Suggest a new feature or enhancement
+labels: Feature
+---
+
+<!-- Write your suggestion here. -->
diff --git a/.github/ISSUE_TEMPLATE/question.md b/.github/ISSUE_TEMPLATE/question.md
new file mode 100644
index 0000000..747f85f
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/question.md
@@ -0,0 +1,7 @@
+---
+name: Question
+about: Ask a question regarding software usage
+labels: Support
+---
+
+<!-- Write your question here. -->
diff --git a/.github/SECURITY.md b/.github/SECURITY.md
new file mode 100644
index 0000000..7d68164
--- /dev/null
+++ b/.github/SECURITY.md
@@ -0,0 +1,6 @@
+# Reporting a vulnerability
+
+If you have found any issues that might have security implications,
+please send a report privately to akihito.koriyama@gmail.com
+
+Do not report security reports publicly.
diff --git a/.github/workflows/coding-standards.yml b/.github/workflows/coding-standards.yml
new file mode 100644
index 0000000..7ba88b1
--- /dev/null
+++ b/.github/workflows/coding-standards.yml
@@ -0,0 +1,41 @@
+name: Coding Standards
+
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  coding-standards:
+    name: Coding Standards
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: 8.0
+          tools: cs2pr
+          coverage: none
+
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+      - name: Cache dependencies
+        uses: actions/cache@v2
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
+          restore-keys: ${{ runner.os }}-composer-
+
+      - name: Install dependencies
+        run: composer install --no-interaction --no-progress --prefer-dist
+
+      - name: Validate composer.json
+        run: composer validate --strict
+
+      - name: Run PHP_CodeSniffer
+        run: ./vendor/bin/phpcs -q --no-colors --report=checkstyle src tests | cs2pr
diff --git a/.github/workflows/continuous-integration.yml b/.github/workflows/continuous-integration.yml
new file mode 100644
index 0000000..20e8b14
--- /dev/null
+++ b/.github/workflows/continuous-integration.yml
@@ -0,0 +1,61 @@
+name: Continuous Integration
+
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
+  schedule:
+    - cron: '42 15 * * *'
+
+jobs:
+  phpunit:
+    name: PHPUnit
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        operating-system:
+          - ubuntu-latest
+        php-version:
+          - '7.3'
+          - '7.4'
+          - '8.0'
+        dependencies:
+          - lowest
+          - highest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v1
+
+      - name: Setup PHP ${{ matrix.php-version }}
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php-version }}
+          coverage: pcov
+          ini-values: zend.assertions=1
+
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+      - name: Cache dependencies
+        uses: actions/cache@v2
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
+          restore-keys: ${{ runner.os }}-composer-
+
+      - name: Install lowest dependencies
+        if: ${{ matrix.dependencies == 'lowest' }}
+        run: composer update --prefer-lowest --no-interaction --no-progress --no-suggest
+
+      - name: Install highest dependencies
+        if: ${{ matrix.dependencies == 'highest' }}
+        run: composer update --no-interaction --no-progress --no-suggest
+
+      - name: Run test suite
+        run: ./vendor/bin/phpunit --coverage-clover=coverage.xml
+
+      - name: Upload coverage report
+        uses: codecov/codecov-action@v1
+        with:
+          file: ./coverage.xml
diff --git a/.github/workflows/static-analysis.yml b/.github/workflows/static-analysis.yml
new file mode 100644
index 0000000..b14f27c
--- /dev/null
+++ b/.github/workflows/static-analysis.yml
@@ -0,0 +1,113 @@
+name: Static Analysis
+
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  static-analysis-phpstan:
+    name: Static Analysis with PHPStan
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: 8.0
+          tools: cs2pr
+          coverage: none
+
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+      - name: Cache dependencies
+        uses: actions/cache@v2
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
+          restore-keys: ${{ runner.os }}-composer-
+
+      - name: Install dependencies
+        run: composer install --no-interaction --no-progress --prefer-dist
+
+      - name: Run PHPStan
+        run: ./vendor/bin/phpstan analyse -c phpstan.neon --no-progress --no-interaction --error-format=checkstyle | cs2pr
+
+  static-analysis-psalm:
+    name: Static Analysis with Psalm
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: 8.0
+          tools: cs2pr
+          coverage: none
+
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+      - name: Install dependencies
+        run: composer install --no-interaction --no-progress --prefer-dist
+
+      - name: Run Psalm
+        run: ./vendor/bin/psalm --show-info=false --output-format=checkstyle --shepherd | cs2pr
+
+  static-analysis-phpmd:
+    name: Static Analysis with PHPMD
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: 7.4
+
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+      - name: Cache dependencies
+        uses: actions/cache@v2
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
+          restore-keys: ${{ runner.os }}-composer-
+
+      - name: Install dependencies
+        run: composer install --no-interaction --no-progress --prefer-dist
+
+  static-analysis-composer-require-checker:
+    name: Static Analysis with ComposerRequireChecker
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: 8.0
+          coverage: none
+
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+      - name: Install dependencies
+        run: |
+          composer install --no-interaction --no-progress --prefer-dist
+          composer require --dev maglnet/composer-require-checker ^3.0
+
+      - name: Run composer-require-checker
+        run: ./vendor/bin/composer-require-checker check ./composer.json
diff --git a/.gitignore b/.gitignore
index 6a5f138..59904aa 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,9 +1,7 @@
+/.phpunit.result.cache
+/.phpcs-cache
 /vendor/
+/vendor-bin/tools/vendor/
 /build/
-/.idea/
-
-/composer.lock
 /phpunit.xml
-/.phpunit.result.cache
-/.php_cs.cache
-.phpcs-cache
+composer.lock
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index 547a552..0000000
--- a/.travis.yml
+++ /dev/null
@@ -1,55 +0,0 @@
-language: php
-
-php:
-  - 7.2
-  - 7.3
-  - 7.4
-
-cache:
-  directories:
-    - ./vendor
-    - $HOME/.composer/cache
-
-before_install:
-  - mv ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/xdebug.ini{,.disabled} || echo "xdebug not available"
-  - composer validate
-  - composer self-update
-
-install:
-  - composer update
-
-script:
-  - ./vendor/bin/phpunit;
-
-jobs:
-  fast_finish: true
-  include:
-  - stage: Test
-    name: Lowest dependencies
-    php: 7.4
-    install: composer update --prefer-dist --prefer-lowest
-
-  - stage: Code Quality
-    name: Code coverage
-    php: 7.4
-    before_script:
-    - mv ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/xdebug.ini{.disabled,}
-    - if [[ ! $(php -m | grep -si xdebug) ]]; then echo "xdebug required for coverage"; exit 1; fi
-    script:
-    - ./vendor/bin/phpunit -v --coverage-clover ./build/logs/clover.xml
-    after_script:
-    - wget https://scrutinizer-ci.com/ocular.phar && php ocular.phar code-coverage:upload --format=php-clover coverage.clover;
-
-  - stage: Code Quality
-    name: Static analysis
-    php: 7.4
-    script:
-      - ./vendor/bin/phpstan analyse -c phpstan.neon --no-progress --no-interaction;
-      - ./vendor/bin/psalm --show-info=false
-      - ./vendor/bin/phpmetrics --exclude=Exception src
-
-  - stage: Code Quality
-    name: Coding standards
-    php: 7.4
-    script:
-      - ./vendor/bin/phpcs
diff --git a/composer.json b/composer.json
index f6e60de..19a4611 100644
--- a/composer.json
+++ b/composer.json
@@ -9,18 +9,18 @@
         }
     ],
     "require": {
-        "php": ">=7.2.0",
+        "php": "^7.3 || ^8.0",
         "vlucas/phpdotenv": "^5.1"
     },
     "require-dev": {
-        "phpunit/phpunit": "^8.5",
-        "squizlabs/php_codesniffer": "^3.5",
-        "friendsofphp/php-cs-fixer": "^2.16",
-        "phpmd/phpmd": "^2.8",
+        "phpunit/phpunit": "^9.5",
+        "doctrine/coding-standard": "^9.0",
+        "phpmd/phpmd": "^2.10",
         "phpstan/phpstan": "^0.12",
-        "vimeo/psalm": "^3.8",
-        "phpmetrics/phpmetrics": "^2.6",
-        "doctrine/coding-standard": "^8.1"
+        "psalm/plugin-phpunit": "^0.15",
+        "slevomat/coding-standard": "^7.0",
+        "squizlabs/php_codesniffer": "^3.6",
+        "vimeo/psalm": "^4.7"
     },
     "autoload": {
         "psr-4": {
@@ -41,13 +41,12 @@
         ],
         "tests": [
             "@cs",
-            "./vendor/bin/phpmd src,tests text ./phpmd.xml",
             "./vendor/bin/phpstan analyse -c phpstan.neon --no-progress",
             "./vendor/bin/psalm",
             "@test"
         ],
         "coverage": [
-            "php -dzend_extension=xdebug.so ./vendor/bin/phpunit --coverage-text --coverage-html=build/coverage"
+            "php -dzend_extension=xdebug.so -dxdebug.mode=coverage ./vendor/bin/phpunit --coverage-text --coverage-html=build/coverage"
         ],
         "cs": "./vendor/bin/phpcs",
         "cs-fix": "./vendor/bin/phpcbf",
diff --git a/phpcs.xml b/phpcs.xml
index d9826f8..ec9dbb5 100755
--- a/phpcs.xml
+++ b/phpcs.xml
@@ -2,14 +2,16 @@
 <ruleset
         name="BEAR.Skeleton"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-        xsi:noNamespaceSchemaLocation="https://raw.githubusercontent.com/squizlabs/PHP_CodeSniffer/master/phpcs.xsd"
+        xsi:noNamespaceSchemaLocation="vendor-bin/tools/vendor/squizlabs/php_codesniffer/phpcs.xsd"
 >
     <description>BEAR.Skeleton Coding Standard</description>
     <arg name="basepath" value="."/>
     <arg name="extensions" value="php"/>
     <arg name="parallel" value="80"/>
     <arg name="cache" value=".phpcs-cache"/>
-    <arg name="colors"/>
+
+    <!-- PHP version -->
+    <config name="php_version" value="{php_version}"/>
 
     <!-- Ignore warnings, show progress of the run and show sniff names -->
     <arg value="nps"/>
@@ -23,19 +25,24 @@
     <rule ref="PSR12"/>
 
     <!-- Doctrine Coding Standard -->
-    <rule ref="./vendor/doctrine/coding-standard/lib/Doctrine/ruleset.xml">
+    <rule ref="Doctrine">
+        <!-- Inapplicable for this project -->
         <exclude name="Generic.Formatting.MultipleStatementAlignment.NotSame"/>
+        <exclude name="SlevomatCodingStandard.Classes.SuperfluousAbstractClassNaming"/>
+        <exclude name="SlevomatCodingStandard.Classes.SuperfluousExceptionNaming"/>
+        <exclude name="SlevomatCodingStandard.Classes.SuperfluousInterfaceNaming"/>
         <exclude name="Squiz.Strings.DoubleQuoteUsage.ContainsVar"/>
-        <exclude name="SlevomatCodingStandard.Classes.SuperfluousAbstractClassNaming.SuperfluousPrefix"/>
-        <exclude name="SlevomatCodingStandard.Classes.SuperfluousExceptionNaming.SuperfluousSuffix"/>
-        <exclude name="SlevomatCodingStandard.Classes.SuperfluousInterfaceNaming.SuperfluousSuffix"/>
-        <exclude name="SlevomatCodingStandard.Commenting.InlineDocCommentDeclaration.MissingVariable"/>
-        <exclude name="SlevomatCodingStandard.TypeHints.ParameterTypeHint.MissingNativeTypeHint"/>
-        <exclude name="SlevomatCodingStandard.TypeHints.ReturnTypeHint.MissingNativeTypeHint"/>
+        <!-- Exclude files -->
         <exclude-pattern>*/tests/Fake/*</exclude-pattern>
+        <exclude-pattern>*/tmp/*</exclude-pattern>
     </rule>
-
+    
     <!-- Additional Rules -->
+    <rule ref="SlevomatCodingStandard.Namespaces.UnusedUses">
+        <properties>
+            <property name="searchAnnotations" value="true"/>
+        </properties>
+    </rule>
     <rule ref="SlevomatCodingStandard.Commenting.DocCommentSpacing">
         <properties>
             <property name="annotationsGroups" type="array">
diff --git a/phpmd.xml b/phpmd.xml
index eacbfc4..a705e52 100644
--- a/phpmd.xml
+++ b/phpmd.xml
@@ -1,38 +1,23 @@
 <ruleset
+        name="PHPMD rule sets"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns="http://pmd.sf.net/ruleset/1.0.0"
         xsi:schemaLocation="http://pmd.sf.net/ruleset/1.0.0 http://pmd.sf.net/ruleset_xml_schema.xsd"
         xsi:noNamespaceSchemaLocation="http://pmd.sf.net/ruleset_xml_schema.xsd">
-    <!--codesize-->
-    <rule ref="rulesets/codesize.xml/CyclomaticComplexity">
-        <properties>
-            <property name="reportLevel" description="The Cyclomatic Complexity reporting threshold"  value="10"/>
-        </properties>
-    </rule>
-    <rule ref="rulesets/codesize.xml/NPathComplexity" />
-    <rule ref="rulesets/codesize.xml/ExcessiveClassComplexity"/>
-    <rule ref="rulesets/codesize.xml/ExcessiveClassLength"/>
-    <rule ref="rulesets/codesize.xml/ExcessiveMethodLength"/>
-    <rule ref="rulesets/codesize.xml/ExcessiveParameterList"/>
-    <rule ref="rulesets/codesize.xml/ExcessivePublicCount"/>
-    <rule ref="rulesets/codesize.xml/TooManyFields"/>
-    <rule ref="rulesets/codesize.xml/TooManyMethods"/>
+    <description>PHPMD rule sets</description>
+
+    <!-- clean code -->
+    <rule ref="rulesets/cleancode.xml" externalInfoUrl="https://phpmd.org/rules/cleancode.html"/>
+    <!-- codesize -->
+    <rule ref="rulesets/codesize.xml" externalInfoUrl="https://phpmd.org/rules/codesize.html"/>
+    <!--controversial -->
+    <rule ref="rulesets/controversial.xml" externalInfoUrl="https://phpmd.org/rules/controversial.html"/>
     <!--design-->
-    <rule ref="rulesets/design.xml/NumberOfChildren"/>
-    <rule ref="rulesets/design.xml/DepthOfInheritance"/>
-    <rule ref="rulesets/design.xml/CouplingBetweenObjects" />
-    <rule ref="rulesets/design.xml/CountInLoopExpression" />
+    <rule ref="rulesets/design.xml" externalInfoUrl="https://phpmd.org/rules/design.html"/>
     <!--naming-->
-    <rule ref="rulesets/naming.xml/ConstantNamingConventions"/>
-    <rule ref="rulesets/naming.xml/BooleanGetMethodName"/>
+    <rule ref="rulesets/naming.xml" externalInfoUrl="https://phpmd.org/rules/naming.html">
+        <exclude name="ShortVariable"/>
+    </rule>
     <!--unusedcode-->
-    <rule ref="rulesets/unusedcode.xml/UnusedFormalParameter"/>
-    <rule ref="rulesets/unusedcode.xml/UnusedLocalVariable"/>
-    <rule ref="rulesets/unusedcode.xml/UnusedPrivateField"/>
-    <rule ref="rulesets/unusedcode.xml/UnusedPrivateMethod"/>
-    <!--cleancode-->
-    <rule ref="rulesets/cleancode.xml/BooleanArgumentFlag"/>
-    <rule ref="rulesets/cleancode.xml/ElseExpression" />
-    <rule ref="rulesets/cleancode.xml/IfStatementAssignment" />
-    <rule ref="rulesets/cleancode.xml/DuplicatedArrayKey" />
+    <rule ref="rulesets/unusedcode.xml" externalInfoUrl="https://phpmd.org/rules/unusedcode.html"/>
 </ruleset>
diff --git a/phpstan.neon b/phpstan.neon
index 9175a61..13ec8a3 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -3,5 +3,3 @@ parameters:
   paths:
     - src
     - tests
-  ignoreErrors:
-  checkMissingIterableValueType: false
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index b07d809..fb27b69 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,24 +1,13 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="./vendor/phpunit/phpunit/phpunit.xsd"
-         bootstrap="vendor/autoload.php">
-    <testsuites>
-        <testsuite name="Resource">
-            <directory suffix="Test.php">tests/Resource</directory>
-        </testsuite>
-        <testsuite name="Hypermedia">
-            <directory suffix="Test.php">tests/Hypermedia</directory>
-        </testsuite>
-        <testsuite name="HTTP">
-            <directory suffix="Test.php">tests/Http</directory>
-        </testsuite>
-    </testsuites>
-    <filter>
-        <whitelist processUncoveredFilesFromWhitelist="true" addUncoveredFilesFromWhitelist="false">
-            <directory suffix=".php">src</directory>
-            <exclude>
-                <file>src/Bootstrap.php</file>
-            </exclude>
-        </whitelist>
-    </filter>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd" bootstrap="vendor/autoload.php">
+  <coverage processUncoveredFiles="true">
+    <include>
+      <directory suffix=".php">src</directory>
+    </include>
+  </coverage>
+  <testsuites>
+    <testsuite name="BEAR.Dotenv suit test">
+      <directory>tests</directory>
+    </testsuite>
+  </testsuites>
 </phpunit>
diff --git a/tests/DotenvTest.php b/tests/DotenvTest.php
index a6059e2..d522358 100644
--- a/tests/DotenvTest.php
+++ b/tests/DotenvTest.php
@@ -6,9 +6,12 @@
 
 use PHPUnit\Framework\TestCase;
 
+use function getenv;
+
 class DotenvTest extends TestCase
 {
-    protected Dotenv $dotenv;
+    /** @var Dotenv */
+    protected $dotenv;
 
     protected function setUp(): void
     {
@@ -39,4 +42,10 @@ public function testLoadGetEnv(): void
         $this->assertSame(getenv('FOO'), 'BAR');
     }
 
+    public function testLoadNothing(): void
+    {
+        $_ENV = [];
+        $this->dotenv->load(__DIR__ . '/Fake/none');
+        $this->assertArrayNotHasKey('FOO', $_ENV);
+    }
 }
diff --git a/tests/Fake/none/.placeholder b/tests/Fake/none/.placeholder
new file mode 100644
index 0000000..e69de29