Hitting error "cannot insert NULL or update to NULL"

Hi Experts,

I am hitting the error "cannot insert NULL or update to NULL" when doing update sql in hana.

I want to update HOUSE_NO field to NULL if condition meet as following:

UPDATE schema.test

SET HOUSE_NO = NULL WHERE HOUSE_NO = '<>'

Following is the Fuzzy table definition:

CREATE COLUMN TABLE schema.test(                                

"CLIENT"    VARCHAR(3) DEFAULT '001' NOT NULL,            

"GUID"      VARBINARY(16) CS_RAW NOT NULL,                                   

"CITY"      TEXT FUZZY SEARCH INDEX ON FAST PREPROCESS ON,

"COUNTRY"   TEXT FUZZY SEARCH INDEX ON FAST PREPROCESS ON,

"HOUSE_NO"  TEXT FUZZY SEARCH INDEX ON FAST PREPROCESS ON,

PRIMARY KEY ("CLIENT","GUID"))

Hope someone can let me know what i did wrong?

Thanks & Regards,

Alexender