sampler2D triggers schema validation errors in Collada 1.5

[jeanbmar]

Using instance_image on sampler2D triggers validation errors. Something feels off with the schema.
Keeping sampler2D empty validates the schema.

Error:

xmllint --noout --schema http://www.khronos.org/files/collada_schema_1_5 issue.dae
element sampler2D: Schemas validity error : Element '{http://www.collada.org/2008/03/COLLADASchema}sampler2D': Character content is not allowed, because the content type is empty.

Test Case:

<?xml version="1.0" encoding="utf-8"?>
<COLLADA xmlns="http://www.collada.org/2008/03/COLLADASchema" version="1.5.0">
  <asset>
    <contributor>
      <author>issue</author>
      <authoring_tool>issue</authoring_tool>
    </contributor>
    <created>2021-03-24T13:32:13.351Z</created>
    <modified>2021-03-24T13:32:13.351Z</modified>
    <up_axis>Y_UP</up_axis>
  </asset>
  <library_images>
    <image id="sc-3-d-shelly-v-2-01-ktx">
      <init_from>
        <ref>sc3d/shelly_v2_01.ktx</ref>
      </init_from>
    </image>
  </library_images>
  <library_effects>
    <effect id="character_mat-effect">
      <profile_COMMON>
        <newparam sid="sc-3-d-shelly-v-2-01-ktx-sampler">
          <sampler2D>
            <instance_image url="#sc-3-d-shelly-v-2-01-ktx"/>
          </sampler2D>
        </newparam>
        <technique sid="common">
          <phong>
            <emission>
              <color>0 0 0 1</color>
            </emission>
            <ambient>
              <color>0 0 0 1</color>
            </ambient>
            <diffuse>
              <texture texture="sc-3-d-shelly-v-2-01-ktx-sampler" texcoord="UVMap"/>
            </diffuse>
            <index_of_refraction>
              <float>4</float>
            </index_of_refraction>
          </phong>
        </technique>
      </profile_COMMON>
    </effect>
  </library_effects>
  <library_materials>
    <material id="character_mat">
      <instance_effect url="#character_mat-effect"/>
    </material>
  </library_materials>
  <library_visual_scenes>
    <visual_scene id="default-scene">
      <node id="CHARACTER" sid="CHARACTER" type="NODE"></node>
    </visual_scene>
  </library_visual_scenes>
  <scene>
    <instance_visual_scene url="#default-scene"/>
  </scene>
</COLLADA>

People mentioning this problem:

1. https://community.khronos.org/t/load-textures-in-collada-1-5/104653
2. https://community.khronos.org/t/schema-problem-with-sampler2d/6329