Fix NonInteractiveShellRunner for empty args

- Fix issue when empty args resulted runner to
  think it should handle this scenario effectively
  hijacking interactive mode.
- This bug were added by previous rework on #372

Author: jvalkeal

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

@@ -58,14 +58,14 @@ public class NonInteractiveShellRunner implements ShellRunner {
 
 	private Parser lineParser;
 
-	private Function<ApplicationArguments, List<String>> commandsFromInputArgs;
+	private Function<ApplicationArguments, List<String>> commandsFromInputArgs = args -> args
+			.getSourceArgs().length == 0 ? Collections.emptyList()
+					: Collections.singletonList(String.join(" ", args.getSourceArgs()));
 
 	public NonInteractiveShellRunner(Shell shell, ShellContext shellContext) {
 		this.shell = shell;
 		this.shellContext = shellContext;
 		this.lineParser = new DefaultParser();
-		this.commandsFromInputArgs = (args) ->
-				Collections.singletonList(String.join(" ", args.getSourceArgs()));
 	}
 
 	/**

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

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2022 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 org.springframework.boot.DefaultApplicationArguments;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class NonInteractiveShellRunnerTests {
+
+	@Test
+	public void testEmptyArgsDontRun() {
+		NonInteractiveShellRunner runner = new NonInteractiveShellRunner(null, null);
+		DefaultApplicationArguments args = new DefaultApplicationArguments();
+		assertThat(runner.canRun(args)).isFalse();
+	}
+
+	@Test
+	public void testNonEmptyArgsRun() {
+		NonInteractiveShellRunner runner = new NonInteractiveShellRunner(null, null);
+		DefaultApplicationArguments args = new DefaultApplicationArguments("hi");
+		assertThat(runner.canRun(args)).isTrue();
+	}
+}