code: protected final void setAlpha(final float alpha) {
          Condition.INSTANCE.ensureAtLeast(alpha, 0, "The alpha must be at least 0");
          Condition.INSTANCE.ensureAtMaximum(alpha, 1, "The alpha must be at maximum 1");
          this.alpha = alpha;
      }
docs: Sets the alpha, which should be used by the animation.
  
  @param alpha
  The alpha, which should be set, as a {@link Float} value. The alpha must be at least
  0 and at maximum 1