fix: guard against null/undefined in getTag function

[nadeem-cs]

Summary

• Fixes #193 — addEditableTags throws TypeError: Cannot convert undefined or null to object when getTag receives null as the content parameter
• Adds a null guard (content == null) at the top of the getTag function to return an empty object early, preventing Object.entries(null) from throwing
• Adds 6 new test cases covering: null/undefined field values, null/undefined entries, multiple null fields, and nested null objects

Root Cause

In JavaScript, typeof null === "object" evaluates to true. When a field value is null, the switch (typeof value) in getTag matches case "object", and the recursive call to getTag(value, ...) passes null as the content parameter. This causes Object.entries(null) to throw a TypeError.

Test plan

• Existing tests pass (34/34)
• New tests cover null entry, undefined entry, null field values, undefined field values, multiple null fields, and nested null objects
• Verified the exact reproduction case from the issue (getTag(null, 'some.prefix', true, 'en-us', { ...appliedVariants })) no longer throws

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟢	Statements	99.1% (+0.01% 🔼)	659/665
🟢	Branches	91.96% (-0.48% 🔻)	492/535
🟢	Functions	100%	143/143
🟢	Lines	99.35% (+0.01% 🔼)	609/613

Show files with reduced coverage 🔻

St.❔	File	Statements	Branches	Functions	Lines
🟢	entry-editable.ts	97.65% (+0.15% 🔼)	91.74% (-1.95% 🔻)	100%	98.65% (+0.1% 🔼)
🟢	gql.ts	100%	90.91% (-9.09% 🔻)	100%	100%

Test suite run success

412 tests passing in 21 suites.

Report generated by 🧪jest coverage report action from 4be5fb6

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟢	Statements	99.1% (+0.01% 🔼)	659/665
🟢	Branches	91.96% (-0.48% 🔻)	492/535
🟢	Functions	100%	143/143
🟢	Lines	99.35% (+0.01% 🔼)	609/613

Show files with reduced coverage 🔻

St.❔	File	Statements	Branches	Functions	Lines
🟢	entry-editable.ts	97.65% (+0.15% 🔼)	91.74% (-1.95% 🔻)	100%	98.65% (+0.1% 🔼)
🟢	gql.ts	100%	90.91% (-9.09% 🔻)	100%	100%

Test suite run success

412 tests passing in 21 suites.

Report generated by 🧪jest coverage report action from 4be5fb6