Handle empty session file

CHANGELOG.md

@@ -4,7 +4,8 @@ New in 1.19.0
 * Support for sessions via `session*` commands. Similar to other genome
   browsers, ASCIIGenome can save a session to be re-opened later. Sessions are
   saved in a yaml file (default `~/.asciigenome/session.yml`) which is a list
-  of dictionaries (each dictionary is a session). At present, only some basic
+  of dictionaries (each dictionary is a session). If desired, these files
+  should be fairly easy to edit with a text editor. At present, only some basic
   configurations are saved and things could change in the future.
 
   Current session* commands, use `<command> -h` for more detail:

src/main/java/session/SessionHandler.java

@@ -14,6 +14,7 @@
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Paths;
 import java.util.*;
@@ -41,6 +42,11 @@ private static List<Session> read(File sessionYamlFile) throws IOException, Sess
       throw new SessionException(
           "File '" + sessionYamlFile.getAbsolutePath() + "' does not exist or is not readable.");
     }
+    String content =
+        new String(Files.readAllBytes(sessionYamlFile.toPath()), StandardCharsets.UTF_8);
+    if (content.trim().isEmpty()) {
+      return new ArrayList<Session>();
+    }
     InputStream yaml = Files.newInputStream(Paths.get(sessionYamlFile.getPath()));
     List<Session> sessions =
         new YAMLMapper().readValue(yaml, new TypeReference<List<Session>>() {});

src/test/java/samTextViewer/InteractiveInputTest.java

@@ -106,13 +106,13 @@ public void canListCurrentSessionNameAndFile()
 
     ProcessInput pi = processInput(ip, "sessionList", proc);
     assertTrue(
-        Pattern.compile("Session file: .*/.asciigenome/session.yml").matcher(pi.stderr).find());
+        Pattern.compile("Session file: /.*/.asciigenome/session.yml").matcher(pi.stderr).find());
     assertTrue(pi.stderr.contains("Current session: n/a"));
 
     ip.processInput("sessionOpen -f test_data/session.yaml no-fastafile", proc);
     pi = processInput(ip, "sessionList -f test_data/session.yaml no-fastafile", proc);
     assertTrue(
-        Pattern.compile("Session file: .*/test_data/session.yaml").matcher(pi.stderr).find());
+        Pattern.compile("Session file: /.*/test_data/session.yaml").matcher(pi.stderr).find());
     assertTrue(pi.stderr.contains("Current session: no-fastafile"));
   }