Fix internal server error when querying without field #3204

Job	Run time
lint_core	11s
Build frontend unit test image	52s
Build frontend e2e test image	1m 55s
Build backend e2e test image	1m 7s
Lint mwdb-core web sources	1m 48s
Build mwdb-core core image	2m 26s
Perform frontend unit tests	37s
Build mwdb-core web image	31s
Perform backend e2e tests	3m 48s
Perform frontend e2e tests	3m 20s
Push test images on Docker Hub	0s
Push images on Docker Hub	0s
	16m 35s

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