Improve robustness of transforms and filters

[flippingbits]

Let's improve the robustness of our pre-defined filters and transforms by better handling the absence and typing of config values.

For instance, the contain filter should not throw an error in case the config value is absent but just return False.

[flippingbits]

Fixed with d7e5c93983cade8451d40acc87ae8080ff0dbf74