diff --git a/lib/document.js b/lib/document.js
index 6c4b665e56c..e4c71b3327f 100644
--- a/lib/document.js
+++ b/lib/document.js
@@ -79,6 +79,7 @@ function Document(obj, fields, skipId, options) {
     options = skipId;
     skipId = options.skipId;
   }
+  options = Object.assign({}, options);
 
   // Support `browserDocument.js` syntax
   if (this.$__schema == null) {
@@ -92,9 +93,9 @@ function Document(obj, fields, skipId, options) {
   }
 
   this.$__ = new InternalCache();
-  this.$isNew = options && options.isNew != null ? options.isNew : true;
+  this.$isNew = 'isNew' in options ? options.isNew : true;
 
-  if (options && options.priorDoc != null) {
+  if (options.priorDoc != null) {
     this.$__.priorDoc = options.priorDoc;
   }
 
@@ -107,20 +108,18 @@ function Document(obj, fields, skipId, options) {
   }
 
   let defaults = true;
-  if (options && options.defaults !== undefined) {
+  if (options.defaults !== undefined) {
     this.$__.defaults = options.defaults;
     defaults = options.defaults;
   }
 
   const schema = this.$__schema;
 
-  let strict;
   if (typeof fields === 'boolean' || fields === 'throw') {
     this.$__.strictMode = fields;
-    strict = fields;
     fields = undefined;
   } else {
-    strict = schema.options.strict;
+    this.$__.strictMode = schema.options.strict;
     if (fields != null) {
       this.$__.selected = fields;
     }
@@ -170,15 +169,15 @@ function Document(obj, fields, skipId, options) {
   // Function defaults get applied **after** setting initial values so they
   // see the full doc rather than an empty one, unless they opt out.
   // Re: gh-3781, gh-6155
-  if (options && options.willInit && defaults) {
+  if (options.willInit && defaults) {
     if (options.skipDefaults) {
       this.$__.skipDefaults = options.skipDefaults;
     }
   } else if (defaults) {
-    $__applyDefaults(this, fields, exclude, hasIncludedChildren, false, options && options.skipDefaults);
+    $__applyDefaults(this, fields, exclude, hasIncludedChildren, false, options.skipDefaults);
   }
 
-  if (!strict && obj) {
+  if (!this.$__.strictMode && obj) {
     const _this = this;
     const keys = Object.keys(this._doc);
 
diff --git a/lib/helpers/schematype/handleImmutable.js b/lib/helpers/schematype/handleImmutable.js
index 4a7453958e0..cc22c914922 100644
--- a/lib/helpers/schematype/handleImmutable.js
+++ b/lib/helpers/schematype/handleImmutable.js
@@ -40,8 +40,7 @@ function createImmutableSetter(path, immutable) {
     const _value = this.$__.priorDoc != null ?
       this.$__.priorDoc.$__getValue(path) :
       this.$__getValue(path);
-    const strict = this.$__.strictMode == null ? this.$__schema.options.strict : this.$__.strictMode;
-    if (strict === 'throw' && v !== _value) {
+    if (this.$__.strictMode === 'throw' && v !== _value) {
       throw new StrictModeError(path, 'Path `' + path + '` is immutable ' +
         'and strict mode is set to throw.', true);
     }
diff --git a/lib/schema/SubdocumentPath.js b/lib/schema/SubdocumentPath.js
index b3f6442af6d..94a8c588628 100644
--- a/lib/schema/SubdocumentPath.js
+++ b/lib/schema/SubdocumentPath.js
@@ -167,7 +167,7 @@ SubdocumentPath.prototype.cast = function(val, doc, init, priorVal, options) {
     }
     return obj;
   }, null);
-  options = priorVal != null ? Object.assign({}, options, { priorDoc: priorVal }) : options;
+  options = Object.assign({}, options, { priorDoc: priorVal });
   if (init) {
     subdoc = new Constructor(void 0, selected, doc);
     subdoc.$init(val);
diff --git a/lib/schema/documentarray.js b/lib/schema/documentarray.js
index 640d0420060..d69a34af37d 100644
--- a/lib/schema/documentarray.js
+++ b/lib/schema/documentarray.js
@@ -391,6 +391,8 @@ DocumentArrayPath.prototype.cast = function(value, doc, init, prev, options) {
   let selected;
   let subdoc;
 
+  options = options || {};
+
   if (!Array.isArray(value)) {
     if (!init && !DocumentArrayPath.options.castNonArrays) {
       throw new CastError('DocumentArray', value, this.path, null, this);
@@ -405,7 +407,7 @@ DocumentArrayPath.prototype.cast = function(value, doc, init, prev, options) {
 
   // We need to create a new array, otherwise change tracking will
   // update the old doc (gh-4449)
-  if (!options || !options.skipDocumentArrayCast || utils.isMongooseDocumentArray(value)) {
+  if (!options.skipDocumentArrayCast || utils.isMongooseDocumentArray(value)) {
     value = new MongooseDocumentArray(value, this.path, doc);
   }
 
@@ -413,7 +415,7 @@ DocumentArrayPath.prototype.cast = function(value, doc, init, prev, options) {
     value[arrayAtomicsSymbol] = prev[arrayAtomicsSymbol] || {};
   }
 
-  if (options && options.arrayPathIndex != null) {
+  if (options.arrayPathIndex != null) {
     value[arrayPathSymbol] = this.path + '.' + options.arrayPathIndex;
   }
 
diff --git a/lib/schematype.js b/lib/schematype.js
index b868c82de0f..53a687370d4 100644
--- a/lib/schematype.js
+++ b/lib/schematype.js
@@ -1181,7 +1181,6 @@ SchemaType.prototype._castNullish = function _castNullish(v) {
 
 SchemaType.prototype.applySetters = function(value, scope, init, priorVal, options) {
   let v = this._applySetters(value, scope, init, priorVal, options);
-
   if (v == null) {
     return this._castNullish(v);
   }