Fix: Throw a clear error when an SVG lacks dimensions instead of a NullReferenceException

[Shalini-Ashokan]

Note

Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Issue Details

NullReferenceException occurred when building MAUI apps with SVG files that define width and height attributes but lack a viewBox attribute. The error occurred during the Resizetizer’s SVG-to-PNG conversion process. The exception did not clearly indicate what was wrong with the SVG files, making it difficult to diagnose and fix the issue.

Root Cause

SkiaSharp's SVG parser returns a Picture with empty dimensions (Width=0, Height=0) when loading certain SVG files without a viewBox attribute. The code attempted to create an SKImageInfo with these zero dimensions, causing a NullReferenceException when trying to draw.

Description of Change

Added validation in DrawUnscaled method to check if size.IsEmpty before attempting to draw the SVG. When detected, throws InvalidOperationException with a clear message. This provides actionable guidance to users to add the missing viewBox attribute to their SVG files.

Note: The validation currently only protects the downscaling path (scale < 1). The upscaling path (scale >= 1) should also be protected by moving the check earlier in the method.

Validated the behavior in the following platforms

• Android
• Windows
• iOS
• Mac

Issues Fixed

Fixes #32460

Test case

Not able to add a unit test for this scenario, as it passes both with and without the fix because macOS SkiaSharp never returns empty dimensions.
The fix only triggers on Android/iOS, where SkiaSharp returns an empty size for SVGs without a viewBox.
Device tests are not applicable because this is a build-time Resizetizer error that occurs before the app is built.

Output ScreenShot

Before	After
BeforeFix.mov	AfterFix.mov

[dotnet-policy-service]

Hey there @@Shalini-Ashokan! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[Copilot]

Pull request overview

This PR addresses issue #32460 by replacing a confusing NullReferenceException with a clear InvalidOperationException when SVG files lack proper dimensions. The fix adds validation in the DrawUnscaled method to detect when an SVG has empty dimensions and provides an actionable error message to help developers fix their SVG files.

Key Changes

• Added size validation check before creating SKImageInfo to prevent NullReferenceException
• Throws InvalidOperationException with descriptive message when SVG dimensions are empty
• Provides guidance about missing width/height or viewBox attributes in the error message

[Copilot]

The error check only occurs in the scale < 1 branch (downscaling), but the same NullReferenceException can occur in the scale >= 1 branch at line 41 when DrawPicture is called with an empty SVG. The constructor already logs a warning at line 29-30 when this condition is detected, but the error should be thrown earlier or consistently in all code paths to prevent confusing failures. Consider moving this validation to the constructor where it's already being detected, or add the same check in the scale >= 1 branch.

[Copilot]

The error message says "may be missing width/height or viewBox attributes" but according to the PR description, the actual issue is specifically when SVG files have width/height attributes but lack a viewBox attribute. The message should be more precise about what's actually required, for example: "The SVG has no size. Ensure the SVG includes a viewBox attribute or both width and height attributes with valid dimensions."

Suggested change

	throw new InvalidOperationException($"Cannot draw SVG file '{Filename}'. The SVG has no size and may be missing width/height or viewBox attributes.");
	throw new InvalidOperationException($"Cannot draw SVG file '{Filename}'. The SVG has no size. Ensure the SVG includes a viewBox attribute or both width and height attributes with valid dimensions.");

[rmarinho]

🤖 AI Summary

📊 Expand Full Review

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🔍 Pre-Flight — Context & Validation

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📝 Review Session — I modified the fix · d5f2afd

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Issue: #32460 - MAUI Fails To Convert Valid SVG Files Into PNG Files (NullReferenceException)
PR: #33194 - Fix: Throw a clear error when an SVG lacks dimensions instead of a NullReferenceException
Platforms Affected: Android, iOS
Files Changed: 1 implementation file (src/SingleProject/Resizetizer/src/SkiaSharpSvgTools.cs)

Issue Summary

Users encounter a NullReferenceException when building MAUI apps with SVG files that define width and height attributes but lack a viewBox attribute. The error occurs during the Resizetizer's SVG-to-PNG conversion process and doesn't clearly indicate what's wrong with the SVG files.

Root Cause (from PR): SkiaSharp's SVG parser returns a Picture with empty dimensions (Width=0, Height=0) when loading SVG files without a viewBox attribute on Android/iOS platforms. Attempting to draw with those zero dimensions caused NullReferenceException.

Prior Agent Review

A complete 4-phase agent review was posted on December 19, 2025 that:

• Gate could not run (no legitimate platform limitation; macOS SkiaSharp doesn't reproduce the bug)tests
  Final recommendation: REQUEST CHANGES- - -

PR Updates Since Prior Review

Commit d5f2afd (Feb 17, 2026): Author implemented the agent's recommendations:

• Moved size validation to TOP of DrawUnscaled method (lines 42)38
• Now protects BOTH scale >= 1 and scale < 1 branches
• Updated error message to match agent suggestion

Reviewer Disagreements / Inline Comments

File:Line	Reviewer Says	Status
SkiaSharpSvgTools.cs:50 (old)	Error check only in scale < 1 branch, not scale >= 1 FIXED in d5f2afd
SkiaSharpSvgTools.cs:49 (old)	Error message should be more precise FIXED in d5f2afd

Issue Discussion Edge Cases

• SetTrend (issue author): Suggested using x, y, width, height attributes if viewBox isn't provided, since viewBox is optional per SVG spec. Current error message accommodates this: "viewBox attribute or both width and height attributes with valid dimensions."

Test Status

No automated tests can be added (documented by PR author and confirmed by prior agent review):

• Bug only manifests on Android/iOS where SkiaSharp returns empty dimensions for SVGs without viewBox
  unit tests always pass regardless of fix
  device tests are not applicable

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #33194	Add size.IsEmpty check at TOP of DrawUnscaled, throw InvalidOperationException with clear PENDING (Gate)	SkiaSharpSvgTools.cs (+5/-3)	Protects BOTH scale improved since prior review	paths message

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🚦 Gate — Test Verification

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📝 Review Session — I modified the fix · d5f2afd

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** NO TESTS AVAILABLEResult:**
Platform: N/A (Build-time error, platform-specific behavior)
Mode: N/A

Test Status

No automated tests exist and cannot be added for this PR.

Per the PR author:

"Not able to add a unit test for this scenario, as it passes both with and without the fix because macOS SkiaSharp never returns empty dimensions. The fix only triggers on Android/iOS, where SkiaSharp returns an empty size for SVGs without a viewBox. Device tests are not applicable because this is a build-time Resizetizer error that occurs before the app is built."

This was confirmed by the prior agent review (December 19, 2025) and verified by inspection of SkiaSharpSvgToolsTests.cs.

Why Tests Cannot Be Added

1. Platform-specific SkiaSharp behavior: The bug only manifests on Android/iOS where SkiaSharp returns empty dimensions for SVGs without viewBox. macOS SkiaSharp always returns non-empty dimensions.
2. Build-time error: This is a Resizetizer error during project compilation, before any app is deployed. Device tests are not applicable.
3. Testing environment limitation: Unit tests run on macOS where the SkiaSharp behavior doesn't reproduce the bug.

Decision: Proceed to Code Review

Gate cannot be validated through automated tests. This is a legitimate platform limitation (not an environment blocker). The fix quality is assessed through code review and manual testing documented by the PR author.

Proceeding to Fix analysis and Report phases per autonomous execution policy.

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🔧 Fix — Analysis & Comparison

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📝 Review Session — I modified the fix · d5f2afd

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Fix Exploration Status

** Cannot validate fixesSKIPPED Status:**

Reason for Skipping

The try-fix skill requires tests that:

1. FAIL without the fix
2. PASS with the fix

For this PR, that is impossible because:

• Unit tests run on macOS where SkiaSharp never returns empty dimensions
• Tests pass both with and without the fix on macOS (the CI/testing environment)
• The bug only reproduces on Android/iOS at build-time (Resizetizer), not at test-time

Running try-fix would produce meaningless results: any change that compiles would appear to "pass" the tests regardless of correctness. This is the same platform limitation that prevented Gate from running.

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #33194	Add check at top of , throw	Code Review PASSED	SkiaSharpSvgTools.cs (+5/-3)	Protects both scale paths, implements prior review feedback

Exhausted: N/ try-fix cannot be run meaningfully for this build-time/platform-specific bugA
Selected Fix: PR's code review confirms it correctly addresses the issueimplementation

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📋 Report — Final Recommendation

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📝 Review Session — I modified the fix · d5f2afd

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Final Recommendation: APPROVE

Summary

PR #33194 fixes a build-time NullReferenceException in Resizetizer's SVG-to-PNG conversion that occurs when SVG files define width/height attributes but lack a viewBox attribute (Android/iOS platforms only). The fix adds validation at the top of DrawUnscaled to detect empty SVG dimensions and throw a clear, actionable InvalidOperationException.

The PR author has fully implemented the recommendations from a prior agent review (Dec 19, 2025), which requested changes specifically because the validation only protected the downscaling path. The current code now protects both scale paths.

Root Cause

SkiaSharp's SVG parser returns a Picture with empty dimensions (Width=0, Height=0) on Android/iOS when loading SVG files without a viewBox attribute. The code then attempted to:
NullReferenceException
NullReferenceException

Neither path had size validation before the fix.

Fix Analysis

Code change (5 lines added, 3 removed):

public override void DrawUnscaled(SKCanvas canvas, float scale)
{
    var size = GetOriginalSize();
    if (size.IsEmpty)  // NEW: validates BEFORE any drawing
    {
        throw new InvalidOperationException($"Cannot draw SVG file '{Filename}'. The SVG has no size. Ensure the SVG includes a viewBox attribute or both width and height attributes with valid dimensions.");
    }
    if (scale >= 1)
    {
        canvas.DrawPicture(svg.Picture, Paint);  // NOW PROTECTED 
    }
    else
    {
        var info = new SKImageInfo((int)size.Width, (int)size.Height);  // NOW PROTECTED 

Why this is the correct fix:

• Fail-fast at the right level of abstraction
• Error message includes filename, root cause, and solution
• InvalidOperationException is semantically correct
• Consolidates the GetOriginalSize() call (was duplicated before)
• Zero regression silent path unchanged on macOS/Windows where SkiaSharp never returns empty dimensionsrisk

Gate Status

NO TESTS Legitimate platform limitation:AVAILABLE** **

• Bug only manifests on Android/iOS where SkiaSharp returns empty dimensions for SVGs without viewBox
  unit tests pass both with/without fix
  device tests not applicable
• Manual validation by PR author on all 4 platforms (Android, iOS, Windows, Mac)

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #33194	guard at top of , throw	Code Review PASSED	SkiaSharpSvgTools.cs (+5/-3)	Both scale paths protected

Exhausted: N/ try-fix cannot be meaningfully run (tests pass both with/without fix on macOS)A
Selected Fix: PR's implementation

PR Title & Description

Title no change requiredAccurate :

** One stale note needs removal:Description:**

The "Note:" paragraph at the end of "Description of Change" says validation only protects the downscaling this was the bug identified in the prior review and has since been fixed. Remove this paragraph.path

Comparison to Prior Review

Aspect	Prior Review (Dec 19, 2025)	Current (Feb 17, 2026)
Critical issue ( 1 Not fixed FIXED		unprotected)
Code Duplicate GetOriginalSize Single call	()	structure
REQUEST CHANGES APPROVE		Recommendation

Required Action Before Merge

Remove the outdated "Note:" paragraph from the PR description's "Description of Change" section. Everything else is accurate.

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📋 Expand PR Finalization Review

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Title: ✅ Good

Current: Fix: Throw a clear error when an SVG lacks dimensions instead of a NullReferenceException

Description: ✅ Good

Description needs updates. See details below.

✨ Suggested PR Description

[!NOTE]
Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Issue Details

NullReferenceException occurred when building MAUI apps with SVG files that lack a viewBox attribute. The error occurred during the Resizetizer's SVG-to-PNG conversion process and did not clearly indicate what was wrong with the SVG files, making it difficult to diagnose and fix.

Root Cause

SkiaSharp's SVG parser returns a Picture with empty dimensions (Width=0, Height=0) when loading SVG files without a viewBox attribute. The code then attempted to create an SKImageInfo with zero dimensions, causing SKSurface.Create(info) to return null. Accessing surface.Canvas on that null reference produced the NullReferenceException.

Description of Change

Added validation at the top of DrawUnscaled to check size.IsEmpty before attempting to draw the SVG. When an empty size is detected, an InvalidOperationException is thrown with a clear, actionable message. By placing the check before the if (scale >= 1) branch, both the upscaling and downscaling code paths are protected.

Key change in SkiaSharpSvgTools.cs:

• GetOriginalSize() is now called at the start of DrawUnscaled
• Throws InvalidOperationException with a clear message if the SVG has empty dimensions
• Both scale >= 1 (vector draw) and scale < 1 (raster downscale) paths are guarded

Test Case

Not able to add a unit test for this scenario, as it passes both with and without the fix because macOS SkiaSharp never returns empty dimensions.
The fix only triggers on Android/iOS, where SkiaSharp returns an empty size for SVGs without a viewBox.
Device tests are not applicable because this is a build-time Resizetizer error that occurs before the app is built.

Platforms Tested

• Android
• iOS
• Windows
• Mac

Issues Fixed

Fixes #32460

Code Review: ✅ Passed

Code Review — PR #33194

File: src/SingleProject/Resizetizer/src/SkiaSharpSvgTools.cs

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Critical Issues

None.

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Looks Good

Fix is correct and complete.

The IsEmpty check is placed at the very beginning of DrawUnscaled, before both the scale >= 1 (vector draw) and scale < 1 (raster downscale) branches. Both code paths are protected from the NullReferenceException caused by zero-dimension SVGs.

Error message is accurate and actionable:

"Cannot draw SVG file '{Filename}'. The SVG has no size. Ensure the SVG includes a viewBox attribute or both width and height attributes with valid dimensions."

This matches the reviewer's suggestion and is an improvement over the previous version ("may be missing width/height or viewBox attributes").

Variable reuse is clean: size is now computed once at the top of the method and reused in the else branch, eliminating the previous duplication.

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Suggestions (minor, non-blocking)

Stale log message wording in constructor (lines 29-30):

if (pic.CullRect.Size.IsEmpty)
    Logger?.Log($"SVG picture did not have a size and will fail to generate. ({Filename})");

Now that DrawUnscaled throws a clear InvalidOperationException, the phrase "will fail to generate" is slightly misleading — the build will now fail with a clear, actionable error rather than a cryptic NullReferenceException. This is a minor wording opportunity only, not a correctness issue.

Suggested wording: "SVG picture has no size and will throw an error during generation. ({Filename})"

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Summary

Category	Finding
Fix correctness	Both scale paths protected — correct
Error message	Accurate and actionable
Code cleanliness	Variable reuse, removed duplication
Constructor log	Minor wording opportunity (not a bug)

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