sfeos

Fix IsNull operator #845

Job	Run time
Python 3.8 testing with elasticsearch7	1m 54s
Python 3.8 testing with elasticsearch8	2m 5s
Python 3.8 testing with opensearch	1m 55s
Python 3.9 testing with elasticsearch7	1m 47s
Python 3.9 testing with elasticsearch8	1m 48s
Python 3.9 testing with opensearch	1m 44s
Python 3.10 testing with elasticsearch7	1m 49s
Python 3.10 testing with elasticsearch8	1m 55s
Python 3.10 testing with opensearch	1m 46s
Python 3.11 testing with elasticsearch7	2m 14s
Python 3.11 testing with elasticsearch8	2m 16s
Python 3.11 testing with opensearch	2m 17s
Python 3.12 testing with elasticsearch7	1m 49s
Python 3.12 testing with elasticsearch8	1m 52s
Python 3.12 testing with opensearch	1m 52s
	29m 3s

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