[Bug]: bal pack crashes when [[dependency]] section is missing in the CompilerPlugin.toml file

[gabilang]

Description

$Subject
When a Ballerina project has CompilerPlugin.toml file with no [[dependency]] sections specified, executing bal pack gives the following crash log:

[2023-09-20 15:19:48,152] SEVERE {b7a.log.crash} - Index 0 out of bounds for length 0 
java.lang.IndexOutOfBoundsException: Index 0 out of bounds for length 0
        at java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:64)
        at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Preconditions.java:70)
        at java.base/jdk.internal.util.Preconditions.checkIndex(Preconditions.java:266)
        at java.base/java.util.Objects.checkIndex(Objects.java:361)
        at java.base/java.util.ArrayList.get(ArrayList.java:427)
        at io.ballerina.projects.JBallerinaBalaWriter.addCompilerPlugin(JBallerinaBalaWriter.java:121)
        at io.ballerina.projects.BalaWriter.populateBalaArchive(BalaWriter.java:135)
        at io.ballerina.projects.BalaWriter.write(BalaWriter.java:108)
        at io.ballerina.projects.JBallerinaBackend.emitBala(JBallerinaBackend.java:241)
        at io.ballerina.projects.JBallerinaBackend.emit(JBallerinaBackend.java:218)
        at io.ballerina.cli.task.CreateBalaTask.execute(CreateBalaTask.java:79)
        at io.ballerina.cli.TaskExecutor.executeTasks(TaskExecutor.java:40)
        at io.ballerina.cli.cmd.PackCommand.execute(PackCommand.java:256)
        at java.base/java.util.Optional.ifPresent(Optional.java:178)
        at io.ballerina.cli.launcher.Main.main(Main.java:58)

Steps to Reproduce

Add an empty CompilerPlugin.toml file or with only [plugin] section to a Ballerina project.

CompilerPlugin.toml

[plugin]
id = "id"
class = "path.to.class"

Affected Version(s)

ballerina-lang master, update-8 RC1
NPE observed with earlier versions when an empty CompilerPlugin.toml file added.

OS, DB, other environment details and versions

No response

Related area

-> Compilation

Related issue(s) (optional)

No response

Suggested label(s) (optional)

No response

Suggested assignee(s) (optional)

No response

[azinneera]

@Shadow-Devil Assigning you to this as requested in issue #42120

[azinneera]

@Shadow-Devil can you comment on this issue so that I can assign you?

[Shadow-Devil]

Sure, please assign me :)

[github-actions]

This issue is NOT closed with a proper Reason/ label. Make sure to add proper reason label before closing. Please add or leave a comment with the proper reason label now.

      - Reason/EngineeringMistake - The issue occurred due to a mistake made in the past.
      - Reason/Regression - The issue has introduced a regression.
      - Reason/MultipleComponentInteraction - Issue occured due to interactions in multiple components.
      - Reason/Complex - Issue occurred due to complex scenario.
      - Reason/Invalid - Issue is invalid.
      - Reason/Other - None of the above cases.