Calling .includes on null causes a crash. This resolves that behavior.

defaultMethods.js

@@ -47,7 +47,7 @@ const defaultMethods = {
   '%': (data) => data.reduce((a, b) => +a % +b),
   max: (data) => Math.max(...data),
   min: (data) => Math.min(...data),
-  in: ([item, array]) => array.includes(item),
+  in: ([item, array]) => (array || []).includes(item),
   '>': ([a, b]) => a > b,
   '<': ([a, b, c]) => (c === undefined ? a < b : a < b && b < c),
   preserve: {
@@ -725,7 +725,7 @@ defaultMethods.or.compile = function (data, buildState) {
 // @ts-ignore Allow custom attribute
 defaultMethods.in.compile = function (data, buildState) {
   if (Array.isArray(data)) {
-    return `(${buildString(data[1], buildState)}).includes(${buildString(
+    return `(${buildString(data[1], buildState)} || []).includes(${buildString(
       data[0],
       buildState
     )})`

general.test.js

@@ -134,4 +134,18 @@ describe('Various Test Cases', () => {
     for (const engine of [...normalEngines, ...permissiveEngines]) await testEngine(engine, { var: '\\foo' }, { '\\foo': 2 }, 2)
     for (const engine of [...normalEngines, ...permissiveEngines]) await testEngine(engine, { var: '\\\\foo' }, { '\\foo': 2 }, 2)
   })
+
+  it('should be able to handle various instances of "in" with good, bad and invalid data', async () => {
+    const rule = {
+      in: ['Spring', { var: 'city' }]
+    }
+
+    const goodData = { city: 'Springfield' }
+    const badData = { city: 'test' }
+    const invalidData = { city: null }
+
+    for (const engine of normalEngines) await testEngine(engine, rule, goodData, true)
+    for (const engine of normalEngines) await testEngine(engine, rule, badData, false)
+    for (const engine of normalEngines) await testEngine(engine, rule, invalidData, false)
+  })
 })