jstree/children endpoint returns 500 for V1 (legacy) API

[Pooya-Oladazimi]

Describe the bug The call to fetch the children for a term in the term tree returns 500.

To Reproduce Examples:

https://www.ebi.ac.uk/ols4/api/ontologies/agro/terms/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FPCO_0000031/jstree/children/3

https://www.ebi.ac.uk/ols4/api/ontologies/ngbo/terms/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FBFO_0000001/jstree/children/0

https://www.ebi.ac.uk/ols4/api/ontologies/agro/properties/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FRO_0000053/jstree/children/3

Expected behavior Legacy API calls should work.

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