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.
- Backport #763
- Fixes #764

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 @@ else if (!isEscapeChar(line, i)) {
 		}
 
 		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();
 		}

spring-shell-core/src/test/java/org/springframework/shell/jline/ExtendedDefaultParserTests.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.shell.jline;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ExtendedDefaultParserTests {
+
+	@Test
+	void wordsParsing() {
+		ExtendedDefaultParser parser = new ExtendedDefaultParser();
+
+		assertThat(parser.parse("one", 0).words()).hasSize(1);
+		assertThat(parser.parse("one", 3).words()).hasSize(1);
+
+		assertThat(parser.parse("one two", 0).words()).hasSize(2);
+		assertThat(parser.parse("one two", 7).words()).hasSize(2);
+
+		assertThat(parser.parse("'one'", 0).words()).hasSize(1);
+		assertThat(parser.parse("'one'", 5).words()).hasSize(1);
+
+		assertThat(parser.parse("'one' two", 0).words()).hasSize(2);
+		assertThat(parser.parse("'one' two", 9).words()).hasSize(2);
+
+		assertThat(parser.parse("one 'two'", 0).words()).hasSize(2);
+		assertThat(parser.parse("one 'two'", 9).words()).hasSize(2);
+
+		assertThat(parser.parse("\"one\"", 0).words()).hasSize(1);
+		assertThat(parser.parse("\"one\"", 5).words()).hasSize(1);
+
+		assertThat(parser.parse("\"one\" two", 0).words()).hasSize(2);
+		assertThat(parser.parse("\"one\" two", 9).words()).hasSize(2);
+
+		assertThat(parser.parse("one \"two\"", 0).words()).hasSize(2);
+		assertThat(parser.parse("one \"two\"", 9).words()).hasSize(2);
+	}
+}