Apply suggestions from code review

Author: tswast

bigframes/core/compile/ibis_compiler/scalar_op_compiler.py

@@ -277,4 +277,4 @@ def isnanornull(arg):
 
 @scalar_op_compiler.register_unary_op(numeric_ops.isfinite_op)
 def isfinite(arg):
-    return arg.isinf().not_() & arg.isnan().not_()
+    return arg.isinf().not_() & arg.isnan().not_() & arg.isnull().not_()

bigframes/core/compile/sqlglot/scalar_compiler.py

@@ -191,5 +191,5 @@ def isnanornull(arg: TypedExpr) -> sge.Expression:
 @scalar_op_compiler.register_unary_op(numeric_ops.isfinite_op)
 def isfinite(arg: TypedExpr) -> sge.Expression:
     return sge.Not(
-        this=sge.Or(this=sge.IsInf(this=arg.expr), right=sge.IsNan(this=arg.expr))
+        this=sge.Or(this=sge.Is(this=expr.expr, expression=sge.Null()), right=sge.Or(this=sge.IsInf(this=arg.expr), right=sge.IsNan(this=arg.expr))
     )