code: public static PreProcessor trim() {
          return mkPreProcessorWithMeta((prefix, data, options) -> {
              logger.debug("trimming '{}'", prefix);
  
              return data.entrySet().stream()
                      .map(e -> {
                          if (!e.getKey().startsWith(prefix)) return e;
                          else {
                              String v = e.getValue();
                              return entry(
                                      e.getKey(),
                                      v != null ? v.trim() : ""
                              );
                          }
                      }).collect(Collectors.toMap(
                              Map.Entry::getKey,
                              Map.Entry::getValue
                      ));
              }, mkExtensionMeta(PRE_PROCESSOR_TRIM));
          }
docs: /////////////////////////////////  pre-defined pre-processors  //////////////////////////