Use packageAt:ifAbsent: in chunk exporter.

#packageAt: is deprecated.

src/Web-Snippets.st

@@ -1,5 +1,5 @@
 Smalltalk createPackage: 'Web-Snippets'!
-(Smalltalk packageAt: 'Web-Snippets') imports: {'amber/jquery/Wrappers-JQuery'. 'amber_core/Platform-DOM'}!
+(Smalltalk packageAt: 'Web-Snippets' ifAbsent: [ self error: 'Package not created: Web-Snippets' ]) imports: {'amber/jquery/Wrappers-JQuery'. 'amber_core/Platform-DOM'}!
 Object subclass: #HTMLSnippet
 	instanceVariableNames: 'snippets'
 	package: 'Web-Snippets'!

src/Web.st

@@ -1,5 +1,5 @@
 Smalltalk createPackage: 'Web'!
-(Smalltalk packageAt: 'Web') imports: {'amber/jquery/Wrappers-JQuery'. 'amber_core/Platform-DOM'}!
+(Smalltalk packageAt: 'Web' ifAbsent: [ self error: 'Package not created: Web' ]) imports: {'amber/jquery/Wrappers-JQuery'. 'amber_core/Platform-DOM'}!
 Object subclass: #HTMLCanvas
 	instanceVariableNames: 'root'
 	package: 'Web'!