check for type of the payload and presence of the discriminator in the payload while validating the discriminator

lib/validation/custom-zschema-validators.js

@@ -126,22 +126,22 @@ function oneOf (report, schema, json) {
 function validateDiscriminator (report, schema, json) {
   var basePolymorphicSchema = schema.oneOf.find(
     s => s.__$refResolved && s.__$refResolved.discriminator !== undefined
-  )
+  );
 
   // if none of the oneOf subschemas has a discriminator, we are not in a polymorphic oneOf.
   if (!basePolymorphicSchema) {
-    return false
+    return false;
   }
-  var discriminatorPropertyName = basePolymorphicSchema.__$refResolved.discriminator
+  var discriminatorPropertyName = basePolymorphicSchema.__$refResolved.discriminator;
 
   // to conform to the Azure specs, we accept a lenient discriminator. if the type is missing in the
   // payload we use the base class. Also if the type doesn't match anything, we use the base class.
   var basePolymorphicSchemaDiscriminatorValue =
-    basePolymorphicSchema.__$refResolved.properties[discriminatorPropertyName].enum[0]
+    basePolymorphicSchema.__$refResolved.properties[discriminatorPropertyName].enum[0];
 
-  var jsonDiscriminatorValue =
+    var jsonDiscriminatorValue =
     json[discriminatorPropertyName] ||
-    basePolymorphicSchemaDiscriminatorValue
+    basePolymorphicSchemaDiscriminatorValue;
 
   var schemaToValidate =
     schema.oneOf.find(
@@ -149,14 +149,22 @@ function validateDiscriminator (report, schema, json) {
         s.__$refResolved &&
         s.__$refResolved.properties[discriminatorPropertyName].enum[0] ===
         jsonDiscriminatorValue
-    ) || basePolymorphicSchema
+    ) || basePolymorphicSchema;
+  
+  var isJsonObject = typeof json === 'object' && json !== null && !Array.isArray(json);
 
-  // if the schema to validate is the base schema, we dont need to validate the discriminator enum value.
-  if (schemaToValidate === basePolymorphicSchema) {
-    json[discriminatorPropertyName] = basePolymorphicSchemaDiscriminatorValue
+  // if the schema to validate is the base schema and the payload is of type object and if the
+  // discriminator property is actually present in the payload then, we do not need to validate
+  // the discriminator enum value.
+  if (
+    schemaToValidate === basePolymorphicSchema &&
+    isJsonObject &&
+    json[discriminatorPropertyName] != undefined
+  ) {
+    json[discriminatorPropertyName] = basePolymorphicSchemaDiscriminatorValue;
   }
-  ZSchemaValidator.validate.call(this, report, schemaToValidate, json)
-  return true
+  ZSchemaValidator.validate.call(this, report, schemaToValidate, json);
+  return true;
 }
 
 function whatIs (what) {
@@ -190,11 +198,11 @@ function whatIs (what) {
 
 function shouldSkipValidate (options, errors) {
   return options &&
-      Array.isArray(options.includeErrors) &&
-      options.includeErrors.length > 0 &&
-      !errors.some(function (err) {
-        return options.includeErrors.includes(err);
-      });
+    Array.isArray(options.includeErrors) &&
+    options.includeErrors.length > 0 &&
+    !errors.some(function (err) {
+      return options.includeErrors.includes(err);
+    });
 }
 
 module.exports.shouldSkipValidate = shouldSkipValidate;