Plugin still throws when a config variable is undefined and a fallback value is provided.

[DToppingWW]

Affects:
serverless-service-config-plugin@1.0.5 - serverless-service-config-plugin@1.1.3
serverless@3.38.0

Replication steps:

• In a serverless.yml change a consul variable to a path that doesn't exist in consul.
• sls package

Expect an error

• Amend this line so that there is a fallback value
• sls package

Unexpected error (same problem as before), the fallback is not used.