NO SNOW: Fix DecFloat schema nullability when SQL simplifier is disabled (#4239)

Co-authored-by: Jamison Rose <Jamison.Rose@snowflake.com>

Author: sfc-gh-bkogan

src/snowflake/snowpark/_internal/analyzer/datatype_mapper.py

@@ -518,8 +518,6 @@ def schema_expression(data_type: DataType, is_nullable: bool) -> str:
             return "PARSE_JSON('NULL') :: VARIANT"
         return "NULL :: " + convert_sp_to_sf_type(data_type)
 
-    if isinstance(data_type, DecFloatType):
-        return "DECFLOAT '0'"
     if isinstance(data_type, _NumericType):
         return "0 :: " + convert_sp_to_sf_type(data_type)
     if isinstance(data_type, StringType):

tests/unit/test_datatype_mapper.py

@@ -770,6 +770,7 @@ def test_schema_expression():
     assert schema_expression(LongType(), False) == "0 :: BIGINT"
     assert schema_expression(FloatType(), False) == "0 :: FLOAT"
     assert schema_expression(DoubleType(), False) == "0 :: DOUBLE"
+    assert schema_expression(DecFloatType(), False) == "0 :: DECFLOAT"
     assert schema_expression(StringType(), False) == "'a' :: STRING"
     assert schema_expression(StringType(19), False) == "'a' ::  STRING (19)"
     assert schema_expression(BooleanType(), False) == "true"