NODE_RED_INSTANCE_NUMBER out of range with 1

[dkastl]

Checklist
Put an x in the boxes that apply

• I have run the latest release.
• I have inspeced the status of docker containers.
• I have run the sanity check described in after-installation.md.
• I have inspected all error messages.
• I have inspected the log files in the /var/log/fiware directory.
• I have run the make collect command.
• I have provided a Github Star to this repository.

Describe the bug

When I specify

NODE_RED_INSTANCE_NUMBER=1

an error is thrown like

error: NODE_RED_INSTANCE_NUMBER out of range (2-20)

However, if the setting is without explicit value

NODE_RED_INSTANCE_NUMBER=

Then 1 instance is created as the default value claims: https://github.com/lets-fiware/FIWARE-Big-Bang/blob/main/config.sh#L314

Your system environment

This is independent from the system environment.

To Reproduce

See above.

Expected behavior

Probably specifying 1 for NODE_RED_INSTANCE_NUMBER should not produce an error and create a single Nodered instance as the default does.

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Server (please complete the following information):

• OS and OS version:
• Docker version:
• Docker Compose version:

Additional context
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[fisuda]

Fixed by the PR #375.