diff --git a/.ruby-version b/.ruby-version
index eca07e4..cd57a8b 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-2.1.2
+2.1.5
diff --git a/lib/errapi/plugins/error_codes.rb b/lib/errapi/plugins/error_codes.rb
index 4971c34..fe191a1 100644
--- a/lib/errapi/plugins/error_codes.rb
+++ b/lib/errapi/plugins/error_codes.rb
@@ -1,9 +1,11 @@
 class Errapi::Plugins::ErrorCodes
   CODES = {
     presence: {
-      blank: 'blank'
+      nil: 'presence.nil',
+      empty: 'presence.empty',
+      blank: 'presence.blank'
     },
-    length: {
+    string_length: {
       wrong_length: 'length.invalid',
       too_short: 'length.tooShort',
       too_long: 'length.tooLong'
@@ -11,7 +13,7 @@ class Errapi::Plugins::ErrorCodes
   }
 
   def build_error error, context
-    if !error.code && CODES.key?(error.validator_name) && code = CODES[error.validator_name][error.message]
+    if !error.code && CODES.key?(error.validator_name) && code = CODES[error.validator_name][error.cause]
       error.code = code
     end
   end
diff --git a/lib/errapi/plugins/messages.rb b/lib/errapi/plugins/messages.rb
index 96e9ff8..6e37669 100644
--- a/lib/errapi/plugins/messages.rb
+++ b/lib/errapi/plugins/messages.rb
@@ -1,17 +1,26 @@
 class Errapi::Plugins::Messages
   MESSAGES = {
     presence: {
+      nil: 'This value cannot be null.',
+      empty: 'This value cannot be empty.',
       blank: 'This value cannot be blank.'
     },
-    length: {
-      wrong_length: 'This value is not the right length.',
-      too_short: 'This value is too short.',
-      too_long: 'This value is too long.'
+    string_length: {
+      wrong_length: 'This string must be exactly %{constraint_length} characters long but has %{constrained_value}.',
+      too_short: 'This string must be at least %{constraint_length} characters long but has only %{constrained_value}.',
+      too_long: 'This string must be at most %{constraint_length} characters long but has %{constrained_value}.'
     }
   }
 
   def build_error error, context
-    if error.message.kind_of?(Symbol) && MESSAGES.key?(error.validator_name) && message = MESSAGES[error.validator_name][error.message]
+    if !error.message && MESSAGES.key?(error.validator_name) && message = MESSAGES[error.validator_name][error.cause]
+
+      %w(constraint_length constrained_value).each do |interpolated|
+        if error.respond_to? interpolated
+          message = message.gsub /\%\{#{interpolated}\}/, interpolated
+        end
+      end
+
       error.message = message
     end
   end
diff --git a/lib/errapi/validators/presence.rb b/lib/errapi/validators/presence.rb
index ede0503..9c59607 100644
--- a/lib/errapi/validators/presence.rb
+++ b/lib/errapi/validators/presence.rb
@@ -4,8 +4,8 @@ def initialize options = {}
   end
 
   def validate value, context, options = {}
-    if value_blank? value
-      context.add_error message: :blank
+    if cause = check(value)
+      context.add_error cause: cause
     end
   end
 
@@ -13,15 +13,23 @@ def validate value, context, options = {}
 
   BLANK_REGEXP = /\A[[:space:]]*\z/
 
+  def check value
+    if value.nil?
+      :nil
+    elsif value.respond_to?(:empty?) && value.empty?
+      :empty
+    elsif value_blank? value
+      :blank
+    end
+  end
+
   def value_blank? value
     if value.respond_to? :blank?
       value.blank?
     elsif value.kind_of? String
       BLANK_REGEXP === value
-    elsif value.respond_to? :empty?
-      value.empty?
     else
-      !value
+      false
     end
   end
 end
diff --git a/lib/errapi/validators/length.rb b/lib/errapi/validators/string_length.rb
similarity index 79%
rename from lib/errapi/validators/length.rb
rename to lib/errapi/validators/string_length.rb
index 78fd86e..f57e83e 100644
--- a/lib/errapi/validators/length.rb
+++ b/lib/errapi/validators/string_length.rb
@@ -1,6 +1,6 @@
 class Errapi::Validators::Length
   CHECKS = { is: :==, minimum: :>=, maximum: :<= }.freeze
-  MESSAGES = { is: :wrong_length, minimum: :too_short, maximum: :too_long }.freeze
+  CAUSES = { is: :wrong_length, minimum: :too_short, maximum: :too_long }.freeze
 
   def initialize options = {}
     @constraints = actual_constraints options
@@ -14,7 +14,7 @@ def validate value, context, options = {}
     CHECKS.each_pair do |key,check|
       next unless check_value = @constraints[key]
       next if actual_length.send check, check_value
-      context.add_error message: MESSAGES[key], check_value: check_value
+      context.add_error cause: CAUSES[key], constraint_value: check_value, constrained_value: actual_length
     end
   end