fix system tests

Author: TrevorBergeron

packages/bigframes/bigframes/core/compile/ibis_compiler/scalar_op_registry.py

@@ -1168,20 +1168,7 @@ def parse_json_op_impl(x: ibis_types.Value, op: ops.ParseJSON):
 def to_json_op_impl(x: ibis_types.Value, op: ops.ToJSON):
     if x.type() == ibis_dtypes.string:
         return parse_json_in_safe(x) if op.safe else parse_json(x)
-    if x.type() == ibis_dtypes.bool:
-        x_bool = typing.cast(
-            ibis_types.StringValue,
-            bigframes.core.compile.ibis_types.cast_ibis_value(
-                x, ibis_dtypes.string, safe=op.safe
-            ),
-        ).lower()
-        return parse_json_in_safe(x_bool) if op.safe else parse_json(x_bool)
-    if x.type() in (ibis_dtypes.int64, ibis_dtypes.float64):
-        x_str = bigframes.core.compile.ibis_types.cast_ibis_value(
-            x, ibis_dtypes.string, safe=op.safe
-        )
-        return parse_json_in_safe(x_str) if op.safe else parse_json(x_str)
-    raise TypeError(f"Cannot cast to JSON from type {x.type()}")
+    return to_json(x)
 
 
 @scalar_op_compiler.register_unary_op(ops.JSONDecode, pass_op=True)

packages/bigframes/bigframes/core/compile/polars/compiler.py

@@ -484,8 +484,13 @@ def _(self, op: ops.ScalarOp, input: pl.Expr) -> pl.Expr:
 
         @compile_op.register(json_ops.ToJSON)
         def _(self, op: ops.ScalarOp, input: pl.Expr) -> pl.Expr:
-            # Polars represents JSON as string, so to_json is cast to String
-            return input.cast(pl.String())
+            # Polars represents JSON as string, so to_json is cast to String.
+            # Handle null values by mapping them to JSON 'null' representation.
+            return (
+                pl.when(input.is_null())
+                .then(pl.lit("null"))
+                .otherwise(input.cast(pl.String()))
+            )
 
         @compile_op.register(arr_ops.ToArrayOp)
         def _(self, op: ops.ToArrayOp, *inputs: pl.Expr) -> pl.Expr:

packages/bigframes/bigframes/core/compile/sqlglot/expressions/json_ops.py

@@ -78,10 +78,8 @@ def _(expr: TypedExpr, op: ops.ToJSON) -> sge.Expression:
     if from_type == dtypes.STRING_DTYPE:
         func_name = "SAFE.PARSE_JSON" if op.safe else "PARSE_JSON"
         return sge.func(func_name, sg_expr)
-    if from_type in (dtypes.INT_DTYPE, dtypes.BOOL_DTYPE, dtypes.FLOAT_DTYPE):
-        sg_expr = sge.Cast(this=sg_expr, to="STRING")
-        return sge.func("PARSE_JSON", sg_expr)
-    raise TypeError(f"Cannot cast from {from_type} to {dtypes.JSON_DTYPE}")
+    else:
+        return sge.func("TO_JSON", sg_expr)
 
 
 @register_unary_op(ops.JSONDecode, pass_op=True)