Declaration variables in shaders

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I wrote a test shader, it worked for the entire scene. But when I apply it to the material, an error appears - “Cannot read property ‘split’ of undefined”

here is the code, what am I doing wrong?

void main(void)
{
 vec3 color = vec3(0.11, 0.34, 0.21);
 gl_FragColor = vec4(color,1.0);
}

Ball.prototype.initialize = function() {
    this.material = new pc.Material();
    var fragmentShader = "precision " + this.app.graphicsDevice.precision + " float;\n";
    fragmentShader = fragmentShader +  this.shader.resource.resource;
    var shaderDefinition = {
        attributes: {
            aUv0: pc.SEMANTIC_TEXCOORD0
        },
       fshader: fragmentShader

    };
    this.sh = new pc.Shader(this.app.graphicsDevice, shaderDefinition)
    this.material.shader = this.sh
    this.entity.model.model.meshInstances[0].material = this.material
};