@Override
        public String toString() {
            if (host.isEmpty() || tenant.isEmpty()) return "No removal candidates exists";
            return String.format(
                    "Failure to remove host %s" +
                    "\n\tNo new host found for tenant %s:" +
                    "\n\t\tSingular Reasons: %s" +
                    "\n\t\tTotal Reasons:    %s",
                    this.host.get().hostname(),
                    this.tenant.get().hostname(),
                    this.allocationFailures.singularReasonFailures().toString(),
                    this.allocationFailures.toString()
            );
        }
Data class used for detailing why removing the given tenant from the given host was unsuccessful.
A failure might not be caused by failing to allocate a specific tenant, in which case the fields
will be empty.
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/CapacityChecker.java