diff --git a/.travis.yml b/.travis.yml
index edab8bd..d8ec128 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,14 +1,12 @@
 language: php
 
-# Required for HHVM, see https://github.com/travis-ci/travis-ci/issues/7712
 dist: trusty
 
 php:
-    - 5.5
     - 5.6
     - 7.0
     - 7.1
-    - hhvm
+    - 7.2
     - nightly
 
 matrix:
@@ -20,7 +18,8 @@ cache:
         - $HOME/.composer/cache
 
 before_install:
-    - if [[ "$TRAVIS_PHP_VERSION" != "5.6" && "$TRAVIS_PHP_VERSION" != "hhvm" ]]; then phpenv config-rm xdebug.ini || true; fi
+    - if [[ "$TRAVIS_PHP_VERSION" != "5.6" ]]; then phpenv config-rm xdebug.ini || true; fi
+    - phpenv config-rm xdebug.ini || true
     - composer selfupdate
 
 install:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3672884..323dd6e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -123,4 +123,4 @@ Improvements:
 - New docs and examples
 
 ## Older versions
-Look at [Github Releases Page](https://github.com/webonyx/graphql-php/releases).
+Look at [GitHub Releases Page](https://github.com/webonyx/graphql-php/releases).
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 872e41b..cce2fb6 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -3,7 +3,7 @@
 ## Workflow
 
 If your contribution requires significant or breaking changes, or if you plan to propose a major new feature,
-we recommend you to create an issue on the [Github](https://github.com/webonyx/graphql-php/issues) with 
+we recommend you to create an issue on the [GitHub](https://github.com/webonyx/graphql-php/issues) with
 a brief proposal and discuss it with us first.
 
 For smaller contributions just use this workflow:
diff --git a/composer.json b/composer.json
index 3b0abab..493767b 100644
--- a/composer.json
+++ b/composer.json
@@ -9,7 +9,7 @@
     "API"
   ],
   "require": {
-    "php": ">=5.5,<8.0-DEV",
+    "php": ">=5.6",
     "ext-mbstring": "*"
   },
   "require-dev": {
@@ -17,8 +17,13 @@
     "psr/http-message": "^1.0"
   },
   "config": {
-    "bin-dir": "bin"
-  },
+    "bin-dir": "bin",
+    "platform": {
+      "php": "5.6.0"
+    },
+    "preferred-install": "dist",
+    "sort-packages": true
+},
   "autoload": {
     "files": ["src/deprecated.php"],
     "psr-4": {
diff --git a/docs/index.md b/docs/index.md
index a10210c..c5c4e66 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -51,5 +51,5 @@ The current version (v0.10) supports all features described by GraphQL specifica
 
 Ready for real-world usage. 
 
-## Github
+## GitHub
 Project source code is [hosted on GitHub](https://github.com/webonyx/graphql-php).
diff --git a/examples/03-server/README.md b/examples/03-server/README.md
index ee36ccb..4737d6e 100644
--- a/examples/03-server/README.md
+++ b/examples/03-server/README.md
@@ -10,10 +10,10 @@ php -S localhost:8080 ./graphql.php
 
 ### Try query
 ```
-curl http://localhost:8080 -d '{"query": "query { echo(message: \"Hello World\") }" }'
+curl -d '{"query": "query { echo(message: \"Hello World\") }" }' -H "Content-Type: application/json" http://localhost:8080
 ```
 
 ### Try mutation
 ```
-curl http://localhost:8080 -d '{"query": "mutation { sum(x: 2, y: 2) }" }'
+curl -d '{"query": "mutation { sum(x: 2, y: 2) }" }' -H "Content-Type: application/json" http://localhost:8080
 ```
diff --git a/src/Type/Schema.php b/src/Type/Schema.php
index 5bda972..bffe726 100644
--- a/src/Type/Schema.php
+++ b/src/Type/Schema.php
@@ -271,11 +271,11 @@ class Schema
 
         foreach ($types as $index => $type) {
             if (!$type instanceof Type) {
-                throw new InvariantViolation(
+                throw new InvariantViolation(sprintf(
                     'Each entry of schema types must be instance of GraphQL\Type\Definition\Type but entry at %s is %s',
                     $index,
                     Utils::printSafe($type)
-                );
+                ));
             }
             yield $type;
         }
diff --git a/src/Validator/DocumentValidator.php b/src/Validator/DocumentValidator.php
index 3efd992..201a850 100644
--- a/src/Validator/DocumentValidator.php
+++ b/src/Validator/DocumentValidator.php
@@ -86,6 +86,12 @@ class DocumentValidator
         if (null === $rules) {
             $rules = static::allRules();
         }
+
+        if (true === is_array($rules) && 0 === count($rules)) {
+            // Skip validation if there are no rules
+            return [];
+        }
+
         $typeInfo = $typeInfo ?: new TypeInfo($schema);
         $errors = static::visitUsingRules($schema, $typeInfo, $ast, $rules);
         return $errors;