Advancement description is required, despite having specific behaviors if it contains no text

Despite advancements with empty descriptions having the specific behavior of not showing a description box in the menu, it is still a required field.

Steps to reproduce:

• Add the following advancement:

  {
      "display": {
          "icon": {
              "item": "minecraft:flower_banner_pattern"
          },
          "title": {
              "text": "Test"
          },
          "description": {
              "text": ""
          },
          "background": "minecraft:textures/gui/advancements/backgrounds/stone.png"
      },
      "criteria": {
          "tick": {
              "trigger": "minecraft:tick"
          }
      }
  }

  {
      "display": {
          "icon": {
              "item": "minecraft:flower_banner_pattern"
          },
          "title": {
              "text": "Test"
          },
          "description": {
              "text": ""
          },
          "background": "minecraft:textures/gui/advancements/backgrounds/stone.png"
      },
      "criteria": {
          "tick": {
              "trigger": "minecraft:tick"
          }
      }
  }

• Observe how the menu shows no description box

• Remove the description field

• Observe how the advancement fails to load.

Expected behavior:

Description can be left out.

Current behavior:
Description is a required field if the display object is provided.