PMREMNode: Handle unresolved PMREM during setup (#33881)

src/nodes/pmrem/PMREMNode.js

@@ -343,7 +343,7 @@ class PMREMNode extends TempNode {
 		// PMREMGenerator renders into a render target with inverted Y, so its output needs the Y
 		// flip on sampling. Externally authored PMREMs follow the standard convention and don't.
 
-		uvNode = this._pmrem.isRenderTargetTexture
+		uvNode = this._pmrem === null || this._pmrem.isRenderTargetTexture
 			? materialEnvRotation.mul( vec3( uvNode.x, uvNode.y.negate(), uvNode.z ) )
 			: materialEnvRotation.mul( uvNode );