sfeos

Fix IsNull operator #849

Job	Run time
Python 3.8 testing with elasticsearch7	1m 44s
Python 3.8 testing with elasticsearch8	1m 58s
Python 3.8 testing with opensearch	1m 53s
Python 3.9 testing with elasticsearch7	1m 52s
Python 3.9 testing with elasticsearch8	1m 50s
Python 3.9 testing with opensearch	1m 53s
Python 3.10 testing with elasticsearch7	1m 44s
Python 3.10 testing with elasticsearch8	1m 44s
Python 3.10 testing with opensearch	1m 49s
Python 3.11 testing with elasticsearch7	2m 22s
Python 3.11 testing with elasticsearch8	2m 9s
Python 3.11 testing with opensearch	2m 7s
Python 3.12 testing with elasticsearch7	1m 43s
Python 3.12 testing with elasticsearch8	1m 47s
Python 3.12 testing with opensearch	1m 40s
	28m 15s

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