fix: exit code if not present

spring-cloud-dataflow-composed-task-runner/src/main/java/org/springframework/cloud/dataflow/composedtaskrunner/support/UnexpectedTaskExecutionException.java

@@ -47,7 +47,7 @@ public class UnexpectedTaskExecutionException extends UnexpectedJobExecutionExce
 	/**
 	 * The recorded exit code for the task.
 	 */
-	private Integer exitCode;
+	private Integer exitCode = -1;
 
 	/**
 	 * User defined name for the task.
@@ -154,6 +154,12 @@ public long getExecutionId() {
 		return this.executionId;
 	}
 
+	/**
+	 * Returns the exit code of the task.
+	 * 
+	 * @return the exit code or -1 if the exit code couldn't be determined
+	 */
+	@Override
 	public int getExitCode() {
 		return this.exitCode;
 	}