code: @Override
      public double getDouble(int index) {
          synchronized (lock) {
              return CBLConverter.asDouble(getMValue(internalArray, index), internalArray);
          }
      }
docs: Gets value at the given index as an double.
  Integers will be converted to double. The value `true` is returned as 1.0, `false` as 0.0.
  Returns 0.0 if the property doesn't exist or does not have a numeric value.
  
  @param index the index. This value must not exceed the bounds of the array.
  @return the double value.