ExtendedDefaultParser should not add empty arguments

- Fixes issue when last "word" is within quotes and
  cursor is at the end of a line which caused empty
  "word" string in an argument list.
- This then caused i.e. string option to have a collection
  as an input(if no arity settings used) and via
  spring conversions a comma were added.
- Fixes #763

spring-shell-core/src/main/java/org/springframework/shell/jline/ExtendedDefaultParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2021 the original author or authors.
+ * Copyright 2017-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -126,10 +126,12 @@ public class ExtendedDefaultParser implements Parser {
 		}
 
 		if (current.length() > 0 || (line != null && cursor == line.length())) {
-			words.add(current.toString());
+			if (current.length() > 0) {
+				words.add(current.toString());
+			}
 		}
 
-		if (line != null && cursor == line.length()) {
+		if (line != null && cursor == line.length() && words.size() > 0) {
 			wordIndex = words.size() - 1;
 			wordCursor = words.get(words.size() - 1).length();
 		}