Bugfix/nullpointer in evaluateNumberOfElementsOf

[lanarimarco]

Description

Corner case where, in some circumstances, jariko throws a NullPointerException in the number of elements evaluation

Related to # (issue)

Checklist:

• If this feature involves RPGLE fixes or improvements, they are well-described in the summary.
• There are tests for this feature.
• RPGLE code used for tests is easily understandable and includes comments that clarify the purpose of this feature.
• The code follows Kotlin conventions (run ./gradlew ktlintCheck).
• The code passes all tests (run ./gradlew check).
• Relevant documentation is included in the docs directory.