Null error when scrolling back to the top

[Momin Ahmad]

══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
The following _TypeError was thrown during performLayout():
Null check operator used on a null value

The relevant error-causing widget was:
  SliverMasonryGrid
  SliverMasonryGrid:file:///X:/AndroidStudioProjects/apnapan/lib/feed/components/posts_list.dart:102:31

When the exception was thrown, this was the stack:
#0      RenderSliverMasonryGrid.performLayout
(package:flutter_staggered_grid_view/src/rendering/sliver_masonry_grid.dart:489:51)
#1      RenderObject.layout (package:flutter/src/rendering/object.dart:2577:7)
#2      RenderViewportBase.layoutChildSequence (package:flutter/src/rendering/viewport.dart:601:13)
#3      RenderViewport._attemptLayout (package:flutter/src/rendering/viewport.dart:1516:12)
#4      RenderViewport.performLayout (package:flutter/src/rendering/viewport.dart:1427:20)
#5      RenderObject._layoutWithoutResize (package:flutter/src/rendering/object.dart:2416:7)
#6      PipelineOwner.flushLayout (package:flutter/src/rendering/object.dart:1051:18)
#7      PipelineOwner.flushLayout (package:flutter/src/rendering/object.dart:1064:15)
#8      RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:577:23)
#9      WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:1138:13)
#10     RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:443:5)
#11     SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1392:15)
#12     SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1313:9)
#13     SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:1171:5)
#14     _invoke (dart:ui/hooks.dart:312:13)
#15     PlatformDispatcher._drawFrame (dart:ui/platform_dispatcher.dart:419:5)
#16     _drawFrame (dart:ui/hooks.dart:283:31)

The following RenderObject was being processed when the exception was fired: RenderSliverMasonryGrid#bffdf
relayoutBoundary=up1 NEEDS-LAYOUT NEEDS-COMPOSITING-BITS-UPDATE:
  needs compositing
  creator: SliverMasonryGrid ← Viewport ← IgnorePointer-[GlobalKey#50b7e] ← Semantics ← Listener ←
    _GestureSemantics ← RawGestureDetector-[LabeledGlobalKey<RawGestureDetectorState>#fd6c9] ←
    Listener ← _ScrollableScope ← _ScrollSemantics-[GlobalKey#6a384] ←
    NotificationListener<ScrollMetricsNotification> ← Transform ← ⋯
  parentData: paintOffset=Offset(0.0, 0.0) (can use size)
  constraints: SliverConstraints(AxisDirection.down, GrowthDirection.forward, ScrollDirection.idle,
    scrollOffset: 225.7, precedingScrollExtent: 4.0, remainingPaintExtent: 914.3, crossAxisExtent:
    403.4, crossAxisDirection: AxisDirection.right, viewportMainAxisExtent: 914.3,
    remainingCacheExtent: 1390.0, cacheOrigin: -225.7)
  geometry: SliverGeometry(scrollExtent: 3316.6, paintExtent: 914.3, maxPaintExtent: 3316.6,
    hasVisualOverflow: true, cacheExtent: 1414.3)
  currently live children: 0 to 11
This RenderObject had the following descendants (showing up to depth 5):
    child with index 0: RenderIndexedSemantics#35b58 relayoutBoundary=up2 NEEDS-PAINT
    NEEDS-COMPOSITING-BITS-UPDATE
      child: RenderRepaintBoundary#9c93e relayoutBoundary=up3 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
        child: RenderConstrainedBox#78b24 relayoutBoundary=up4 NEEDS-PAINT
    child with index 1: RenderIndexedSemantics#898b5 relayoutBoundary=up2 NEEDS-PAINT
    NEEDS-COMPOSITING-BITS-UPDATE
      child: RenderRepaintBoundary#49a75 relayoutBoundary=up3 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
        child: RenderConstrainedBox#c2cdc relayoutBoundary=up4 NEEDS-PAINT
    child with index 2: RenderIndexedSemantics#f301f relayoutBoundary=up2 NEEDS-PAINT
    NEEDS-COMPOSITING-BITS-UPDATE
      child: RenderRepaintBoundary#c7319 relayoutBoundary=up3 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
        child: RenderConstrainedBox#da06f relayoutBoundary=up4 NEEDS-PAINT
    child with index 3: RenderIndexedSemantics#4535c relayoutBoundary=up2 NEEDS-PAINT
    NEEDS-COMPOSITING-BITS-UPDATE
      child: RenderRepaintBoundary#d4123 relayoutBoundary=up3 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
        child: RenderConstrainedBox#e2327 relayoutBoundary=up4 NEEDS-PAINT
    child with index 4: RenderIndexedSemantics#4b89e relayoutBoundary=up2
      child: RenderRepaintBoundary#de96e relayoutBoundary=up3
        child: RenderFlex#4aba9 relayoutBoundary=up4
          child 1: RenderSemanticsAnnotations#80468 relayoutBoundary=up5
            child: RenderPadding#4ebe6 relayoutBoundary=up6
    child with index 5: RenderIndexedSemantics#a9a31 relayoutBoundary=up2
      child: RenderRepaintBoundary#05f4e relayoutBoundary=up3
        child: RenderConstrainedBox#dc7eb relayoutBoundary=up4
    child with index 6: RenderIndexedSemantics#05a86 relayoutBoundary=up2
      child: RenderRepaintBoundary#29eaa relayoutBoundary=up3
        child: RenderConstrainedBox#bf917 relayoutBoundary=up4
    child with index 7: RenderIndexedSemantics#a8280 relayoutBoundary=up2
      child: RenderRepaintBoundary#c744d relayoutBoundary=up3
        child: RenderConstrainedBox#2d657 relayoutBoundary=up4
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