Exception while evaluating template literal used in array assignment in loop.

var a = {'a': 1};
var list = [a, a];
let map1 = {:};
for (var item : list) {
  map1[`${item.a}`] = 1;
} 

Caused by: java.lang.ClassCastException: class org.apache.commons.jexl3.internal.introspection.MapSetExecutor cannot be cast to class org.apache.commons.jexl3.internal.TemplateEngine$TemplateExpression (org.apache.commons.jexl3.internal.introspection.MapSetExecutor and org.apache.commons.jexl3.internal.TemplateEngine$TemplateExpression are in unnamed module of loader 'app')
    at org.apache.commons.jexl3.internal.Interpreter.visit(Interpreter.java:1909)
    at org.apache.commons.jexl3.parser.ASTJxltLiteral.jjtAccept(ASTJxltLiteral.java:54)
    at org.apache.commons.jexl3.internal.Interpreter.executeAssign(Interpreter.java:1558)
    at org.apache.commons.jexl3.internal.Interpreter.visit(Interpreter.java:1319)
    at org.apache.commons.jexl3.parser.ASTAssignment.jjtAccept(ASTAssignment.java:19)
    at org.apache.commons.jexl3.internal.Interpreter.visitBlock(Interpreter.java:615)
    at org.apache.commons.jexl3.internal.Interpreter.visit(Interpreter.java:594)
    at org.apache.commons.jexl3.parser.ASTBlock.jjtAccept(ASTBlock.java:35)
    at org.apache.commons.jexl3.internal.Interpreter.forIterator(Interpreter.java:700)
    at org.apache.commons.jexl3.internal.Interpreter.visit(Interpreter.java:639)