// null_safety.groovy — ?., ?:, safe indexing and avoiding NullPointerException.
def order = [id: 'PO-1', customer: [name: 'Acme', address: null]]

// Safe navigation: stop at null instead of throwing
println order.customer?.address?.city            // null (no exception)
println order.shipTo?.name                       // null: missing key

// Elvis: a default when the value is null or "false"
println order.customer?.address?.city ?: 'no city'

// Elvis assignment (Groovy 3+)
def note = null
note ?= 'default note'
println note

// Safe index on lists and maps
def items = null
println items?[0]                                 // null
println items?.size() ?: 0                        // 0

// with a chain of calls
def email = ' AP@ACME.TEST '
println email?.trim()?.toLowerCase()

// Empty collections are safe to iterate
def lines = order.lines ?: []
lines.each { println it }                         // prints nothing
println "lines: ${lines.size()}"

// Asserting non-null with a helpful message
def requireId(Map o) {
    Objects.requireNonNull(o?.id, 'order id is required')
}
try {
    requireId([:])
} catch (NullPointerException e) {
    println "Caught: ${e.message}"
}