code: function getFilterFn(layer, symbolizer) {
      const symbolizers = Object.keys(layer.shader)
          .filter(property => layer.shader[property].symbolizer === symbolizer);
  
      //No need to set a callback when at least one property is not filtered (i.e. it always activates the symbolizer)
      const alwaysActive = symbolizers
          .reduce((a, property) => a || !layer.shader[property].filtered, false);
  
      if (alwaysActive) {
          return undefined;
      }
  
      const fn = symbolizers
          .map((property) => layer.shader[property].js)
          .reduce((all, arr) => all.concat(arr), [])
          .join('');
  
      return wrapFn(`var _value = null; ${fn} return _value !== null;`);
  }
docs: Returns a function string that dynamically filters symbolizer based on conditional properties