function getBlankImage() {
    if (blankImage !== null) {
        return blankImage;
    }
    blankImage = util_texture.createBlank('rgba(255,255,255,0)').image;
    return blankImage;
}
@param {string} textureName
@param {string|HTMLImageElement|HTMLCanvasElement} imgValue
@param {module:echarts/ExtensionAPI} api
@param {Object} [textureOpts]