fix bug on remove with custom extractField

A bug was preventing proper removal of documents when using a custom
extractField. This commit fixes it.

src/MiniSearch.js

@@ -189,7 +189,9 @@ class MiniSearch {
 
     fields.forEach(field => {
       const fieldValue = extractField(document, field)
-      const tokens = tokenize(fieldValue == null ? '' : fieldValue.toString(), field)
+      if (fieldValue == null) { return }
+
+      const tokens = tokenize(fieldValue.toString(), field)
 
       addFieldLength(this, shortDocumentId, this._fieldIds[field], this.documentCount - 1, tokens.length)
 
@@ -267,8 +269,11 @@ class MiniSearch {
       throw new Error(`MiniSearch: cannot remove document with ID ${id}: it is not in the index`)
     }
 
-    fields.filter(field => getOwnProperty(document, field) != null).forEach(field => {
-      const tokens = tokenize(extractField(document, field) || '', field)
+    fields.forEach(field => {
+      const fieldValue = extractField(document, field)
+      if (fieldValue == null) { return }
+
+      const tokens = tokenize(fieldValue.toString(), field)
 
       tokens.forEach(term => {
         const processedTerm = processTerm(term, field)

src/MiniSearch.test.js

@@ -172,6 +172,22 @@ describe('MiniSearch', () => {
       expect(console.warn).not.toHaveBeenCalled()
     })
 
+    it('removes documents when using a custom extractField', () => {
+      const extractField = (document, fieldName) => {
+        const path = fieldName.split('.')
+        return path.reduce((doc, key) => doc && doc[key], document)
+      }
+      const ms = new MiniSearch({ fields: ['text.value'], storeFields: ['id'], extractField })
+      const document = { id: 123, text: { value: 'Nel mezzo del cammin di nostra vita' } }
+      ms.add(document)
+
+      expect(() => {
+        ms.remove(document)
+      }).not.toThrowError()
+
+      expect(ms.search('vita')).toEqual([])
+    })
+
     it('cleans up the index', () => {
       const originalIdsLength = Object.keys(ms._documentIds).length
       ms.remove(documents[0])