code: public MethodFilter build() {
          if(filters.isEmpty()) {
              throw new IllegalStateException("No filter specified.");
          }
          if(filters.size() == 1) {
              return filters.get(0);
          }
          MethodFilter[] methodFilters = new MethodFilter[filters.size()];
          filters.toArray(methodFilters);
          return new MethodFilterList(methodFilters);
      }
docs: Returns the MethodFilter built.
  
  @return the MethodFilter built.
  @throws IllegalStateException if no filter was specified before calling build()