sfeos

Fix IsNull operator #846

Job	Run time
Python 3.8 testing with elasticsearch7	1m 56s
Python 3.8 testing with elasticsearch8	2m 0s
Python 3.8 testing with opensearch	1m 55s
Python 3.9 testing with elasticsearch7	1m 55s
Python 3.9 testing with elasticsearch8	1m 58s
Python 3.9 testing with opensearch	1m 51s
Python 3.10 testing with elasticsearch7	1m 47s
Python 3.10 testing with elasticsearch8	1m 53s
Python 3.10 testing with opensearch	1m 58s
Python 3.11 testing with elasticsearch7	2m 8s
Python 3.11 testing with elasticsearch8	2m 15s
Python 3.11 testing with opensearch	2m 19s
Python 3.12 testing with elasticsearch7	1m 49s
Python 3.12 testing with elasticsearch8	1m 54s
Python 3.12 testing with opensearch	1m 55s
	29m 33s

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