You can also create a handy utility functions to handle values from DB in cases like these. Ex. Below is the function which gives you Nullable Decimal from object type.
public static decimal? ToNullableDecimal(object val)
{
if (val is DBNull ||
val == null)
{
return null;
}
if (val is string &&
((string)val).Length == 0)
{
return null;
}
return Convert.ToDecimal(val);
}