docs: public static Object concat(Object arr1, Object arr2)
      {
          int len1 = (arr1 == null) ? (-1) : Array.getLength(arr1);
  
          if (len1 <= 0)
          {
              return arr2;
          }
  
          int len2 = (arr2 == null) ? (-1) : Array.getLength(arr2);
  
          if (len2 <= 0)
          {
              return arr1;
          }
  
          Class  commonComponentType =
              commonClass(arr1.getClass().getComponentType(), arr2.getClass().getComponentType());
          Object newArray = Array.newInstance(commonComponentType, len1 + len2);
          System.arraycopy(arr1, 0, newArray, 0, len1);
          System.arraycopy(arr2, 0, newArray, len1, len2);
  
          return newArray;
      }