While executing a background script by impersonating as encryption admin, I am getting an errors

[RakshandaS]

While executing a background script by impersonating as encryption admin, I am getting an errors like 

Couldn't decipher the stack trace resulting from the following JavaScriptException:
java.lang.NullPointerException: Cannot invoke "java.lang.CharSequence.length()" because "this.text" is null: org.mozilla.javascript.JavaScriptException: java.lang.NullPointerException: Cannot invoke "java.lang.CharSequence.length()" because "this.text" is null: 	org.mozilla.javascript.Context.makeJavaScriptException(Context.java:2248)

Please help me if anyone is familiar with this type of issue

[Ankur Bawiskar]

@RakshandaS 

are you trying to impersonate someone who has encryption_admin role?

what's your business requirement to do so?

[RakshandaS]

Yes, I want to encrypt the attachments and few fields on the incident and service request table.