OBJECT_CONSTRUCT function is not working properly - snowflake-cloud-data-platform

Question

output--
I have written the query in snowflake to generate Json file, from the query output want to remove fields which has NULL. OBJECT_CONSTRUCT is not working properly for some column its not passing NULL value where else for some column its giving null value as result.
Input-
Json remove any field which has value NULL or blank.
{"DIFID":122,"DIF_FLAG":"NULL","DIF_TYPE":"asian/white","FOCAL_COUNT":2370,"REFERENCE_COUNT":17304},
Required Output-
Json remove any field which has value NULL or blank.
{"DIFID":122,"DIF_TYPE":"asian/white","FOCAL_COUNT":2370,"REFERENCE_COUNT":17304},
query-
select distinct ITEMSTATID,object_construct(
'DIFID',DIFID,
'DIF_TYPE',DIF_TYPE,
'DIF_FLAG',DIF_FLAG,
'FOCAL_COUNT',FOCAL_COUNT::integer,
'REFERENCE_COUNT',REFERENCE_COUNT::integer,
'DIF_METHOD',DIF_METHOD,
'DIF_VALUE',DIF_VALUE)
DIF
from DEV_IPM.STAGEVAULT.DIF_STATISTICS;

Answer 1

For string column and 'NULL' as string literal column's value is not skipped:
CREATE OR REPLACE TABLE DIF_STATISTICS
AS
SELECT 1 AS ITEMSTATID,
122 AS DIFID,
'NULL' AS DIF_FLAG, -- here
'asian/white' AS DIF_TYPE,
2370 AS FOCAL_COUNT,
17304 AS REFERENCE_COUNT;
Output:
The value is definitely stored as TEXT:
SELECT null AS DIF_FLAG, 'NULL' AS DIF_FLAG;
On the left: true NULL on the right: NULL string
If it the case then it should be nullified NULLIF(DIF_FLAG, 'NULL') before passing to OBJECT_CONSTRUCT function:
SELECT ITEMSTATID,
object_construct(
'DIFID',DIFID,
'DIF_TYPE',DIF_TYPE,
'DIF_FLAG',NULLIF(DIF_FLAG, 'NULL'),
'FOCAL_COUNT',FOCAL_COUNT::integer,
'REFERENCE_COUNT',REFERENCE_COUNT::integer) AS DIF
FROM DIF_STATISTICS;
Previous answer before column details were provided (also plausible):
It is working as intended:
NULL Values
Snowflake supports two types of NULL values in semi-structured data:
SQL NULL: SQL NULL means the same thing for semi-structured data types as it means for structured data types: the value is missing or unknown.
JSON null (sometimes called “VARIANT NULL”): In a VARIANT column, JSON null values are stored as a string containing the word “null” to distinguish them from SQL NULL values.
OBJECT_CONSTRUCT
If the key or value is NULL (i.e. SQL NULL), the key-value pair is omitted from the resulting object. A key-value pair consisting of a not-null string as key and a JSON NULL as value (i.e. PARSE_JSON(‘NULL’)) is not omitted.
For true SQL NULL values, that column is ommitted:
CREATE OR REPLACE TABLE DIF_STATISTICS
AS
SELECT 1 AS ITEMSTATID,
122 AS DIFID,
NULL AS DIF_FLAG,
'asian/white' AS DIF_TYPE,
2370 AS FOCAL_COUNT,
17304 AS REFERENCE_COUNT;
SELECT ITEMSTATID,
object_construct(
'DIFID',DIFID,
'DIF_TYPE',DIF_TYPE,
'DIF_FLAG',DIF_FLAG,
'FOCAL_COUNT',FOCAL_COUNT::integer,
'REFERENCE_COUNT',REFERENCE_COUNT::integer) AS DIF
FROM DIF_STATISTICS;
Output:
Probably the data type of the column DIFID is VARIANT/OBJECT:
CREATE OR REPLACE TABLE DIF_STATISTICS
AS
SELECT 1 AS ITEMSTATID,
122 AS DIFID,
PARSE_JSON('NULL') AS DIF_FLAG, -- here
'asian/white' AS DIF_TYPE,
2370 AS FOCAL_COUNT,
17304 AS REFERENCE_COUNT;
Output: