Replace is_blank with is_empty

Function string.find, that was used in is_blank, can't be JIT-compiled.
Configuration validation should be as fast as possible and is_blank
isn't really necessary here, so get rid of it...

spec/ngx-oauth/util_spec.moon

@@ -58,33 +58,17 @@ describe 'id', ->
     assert.equal value, util.id(value)
 
 
-behaves_like_is_empty = (func) ->
+describe 'is_empty', ->
 
   it 'returns true for nil', ->
-    assert.is_true func(nil)
+    assert.is_true util.is_empty(nil)
 
   it 'returns true for empty string', ->
-    assert.is_true func('')
+    assert.is_true util.is_empty('')
 
   it 'returns false for other types than nil and string', ->
     for value in *{42, true, false, {}, print}
-      assert.is_false func(value)
-
-
-describe 'is_blank', ->
-  behaves_like_is_empty util.is_blank
-
-  it 'returns true for string with whitespaces only', ->
-    for value in *{'  ', '\t\t', '\t'} do
-      assert.is_true util.is_blank(value)
-
-  it 'returns false for string with any non-whitespace char', ->
-    for value in *{'foo', ' foo ', '\tfoo'} do
-      assert.is_false util.is_blank(value)
-
-
-describe 'is_empty', ->
-  behaves_like_is_empty util.is_empty
+      assert.is_false util.is_empty(value)
 
 
 describe 'map', ->

src/ngx-oauth/config.lua

@@ -4,7 +4,7 @@
 local util = require 'ngx-oauth.util'
 
 local contains    = util.contains
-local is_blank    = util.is_blank
+local is_empty    = util.is_empty
 local map         = util.map
 local par         = util.partial
 local starts_with = util.starts_with
@@ -37,11 +37,11 @@ local load_from_ngx = par(map, function(default_value, key)
 local function validate (conf)
   local errors = {}
 
-  if is_blank(conf.client_id) then
+  if is_empty(conf.client_id) then
     table.insert(errors, '$oauth_client_id is not set')
   end
 
-  if is_blank(conf.client_secret) then
+  if is_empty(conf.client_secret) then
     table.insert(errors, '$oauth_client_secret is not set')
   end
 
@@ -74,11 +74,11 @@ local M = {}
 function M.load ()
   local conf = load_from_ngx()
 
-  if is_blank(conf.redirect_uri) then
+  if is_empty(conf.redirect_uri) then
     conf.redirect_uri = ngx.var.scheme..'://'..ngx.var.server_name..conf.redirect_location
   end
 
-  if not is_blank(conf.oaas_uri) then
+  if not is_empty(conf.oaas_uri) then
     for _, key in ipairs(OAAS_ENDPOINT_VARS) do
       conf[key] = conf[key]:gsub('${oaas_uri}', conf.oaas_uri)
     end

src/ngx-oauth/util.lua

@@ -76,14 +76,6 @@ function M.id (value)
   return value
 end
 
---- Returns true if the `value` is nil, empty string or contains at least one
--- character other than space and tab. If the `value` is not nil and
--- string, then it's converted to string.
--- @treturn bool
-function M.is_blank (value)
-  return M.is_empty(value) or tostring(value):find('^%s*$') ~= nil
-end
-
 --- Returns true if the `value` is nil or empty string.
 -- @treturn bool
 function M.is_empty (value)