The following assertion was thrown building:
'package:flutter/src/painting/_network_image_io.dart': Failed assertion: line 22 pos 14: 'url != null': is not true.


Either the assertion indicates an error in the framework itself, or we should provide substantially more information in this error message to help you determine and fix the underlying cause.
In either case, please report this assertion by filing a bug on GitHub:
  https://github.com/flutter/flutter/issues/new?template=BUG.md

When the exception was thrown, this was the stack
#2      new NetworkImage
package:flutter/…/painting/_network_image_io.dart:22
#3      new Image.network
package:flutter/…/widgets/image.dart:354
#4      _BlogAppState.build.<anonymous closure>
package:mywebapp/main.dart:69
#5      SliverChildBuilderDelegate.build
package:flutter/…/widgets/sliver.dart:446
#6      SliverMultiBoxAdaptorElement._build.<anonymous closure>
package:flutter/…/widgets/sliver.dart:1260
...
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