Fix "TypeError: Reduce of empty array with no initial value"

When passed Paragraph node that is empty value, throw "TypeError: Reduce of empty array with no initial value".

Author: azu

src/no-doubled-conjunction.js

@@ -2,7 +2,7 @@
 "use strict";
 import {RuleHelper} from "textlint-rule-helper";
 import {getTokenizer} from "kuromojin";
-import splitSentences, {Syntax as SentenceSyntax} from "sentence-splitter";
+import {split as splitSentences, Syntax as SentenceSyntax} from "sentence-splitter";
 import StringSource from "textlint-util-to-string";
 
 /*
@@ -27,6 +27,11 @@ export default function (context, options = {}) {
             let sentences = splitSentences(text, {
                 charRegExp: /[。\?\!？！]/
             }).filter(isSentenceNode);
+            // if not have a sentence, early return
+            // It is for avoiding error of emptyArray.reduce().
+            if(sentences.length === 0) {
+                return;
+            }
             return getTokenizer().then(tokenizer => {
               const selectConjenction = (sentence) => {
                 let tokens = tokenizer.tokenizeForSentence(sentence.raw);
@@ -43,16 +48,13 @@ export default function (context, options = {}) {
                 }
                 if (current_tokens.length > 0) {
                   if (token && current_tokens[0].surface_form === token.surface_form) {
-                    let originalPosition = source.originalPositionFor({
+                    let originalIndex = source.originalIndexFromPosition({
                       line: sentence.loc.start.line,
                       column: sentence.loc.start.column + (current_tokens[0].word_position - 1)
                     });
                     // padding position
                     var padding = {
-                      line: originalPosition.line - 1,
-                      // matchLastToken.word_position start with 1
-                      // this is padding column start with 0 (== -1)
-                      column: originalPosition.column
+                        index: originalIndex
                     };
                     report(node, new RuleError(`同じ接続詞が連続して使われています。`, padding));
                   }

test/no-doubled-conjunction.js

@@ -1,11 +1,11 @@
-import assert from "power-assert";
 import rule from "../src/no-doubled-conjunction";
 import TextLintTester from "textlint-tester";
 var tester = new TextLintTester();
 tester.run("no-doubled-conjunction", rule, {
     valid: [
         "朝起きた。そして、夜に寝た。",
-        "そして朝起きた。けれど昼は仕事をした。そして夜に寝た。"
+        "そして朝起きた。けれど昼は仕事をした。そして夜に寝た。",
+        "``" // empty Paragraph
     ],
     invalid: [
       {