In Snowflake, default value NULL on a not-nullable column?

In Snowflake, what are the implications of having a default value of null on a non-nullable column? Also, when I describe a particular table in Snowflake, I see a default value of NULL in all columns. When my colleague describes the same table in Snowflake, in the same environment (PROD), they are seeing the default value as null (lower-case) but with all those lower case nulls greyed-out. Anyone out there run into this? What could it mean?