an Error has Occurred Cannot set property muted of null

Go into the interface / expression code, click inside the code, hit Ctrl + F.  This will open search.  Search the word "muted".  This will help you find what is trying to set the "muted" field of some CDT.

What's ultimately happening is that something is attempting to return a CDT.  One of the fields of that CDT is called "muted".  Whenever the thing that tries to return the CDT fails, it returns nothing, AKA null.  Null doesn't have any fields.  So when you try to set the "muted" of this null with no fields, it gets confused. 

So after you find where the code is trying to set a variable's "muted" value to something, go to where that variable is instantiated or queried.  You know that part isn't working.  Your bug is now figuring out why that CDT consistently comes up null. 

One of the things you can do to help isolate is copy all the code to a temporary test interface or rule, then delete everything that does anything but call that CDT into being, and write something that just shows you the contents of that CDT.  Keep messing with whatever part makes the CDT until it's working, then you can try adding all the other code back to see if the whole interface / rule now works.

Thank you David, but I don't have any "muted" variable in my CDTs 

Do you have other CDTs in your CDTs?  It specifically says 'muted', and specifically says it's a property.  It has to be the property of something.

Another thing you can do:

If you've upgraded to 20.1, load the interface by itself and plug in the inputs from the process instance on the same environment to test.  Then look at the list of local variables on the side bar and investigate those that are null.

If you have not upgraded to 20.1:

Copy the code to a temporary file

Remove all the code after the declaration of local variables

Replace it with a textField component, and set that to read Only, and have it display the first local variable

Then update the textField to show the next local variable, and the next, and the next, until you see the one that's null

I'm more confident that one of your local variables is being returned null than any other theory at this point.  You can start your dive from the null local variables you find until you get to the root of the problem, and then you might also fully understand what all this 'muted' business is about as well.

Same error for us. If someone find a solution please help us

Same error for us. If someone find a solution please help us