bug: enum Select crashes when selecting the empty value

.babelrc

@@ -23,6 +23,7 @@
       "corejs": "2"
     }],
     "@babel/plugin-proposal-class-properties",
+    "@babel/plugin-proposal-optional-chaining",
     ["transform-react-remove-prop-types", {
       "additionalLibraries": ["react-immutable-proptypes"]
     }],

package.json

@@ -84,7 +84,7 @@
     "@babel/core": "^7.0.0",
     "@babel/plugin-proposal-class-properties": "^7.5.0",
     "@babel/plugin-proposal-nullish-coalescing-operator": "^7.0.0",
-    "@babel/plugin-proposal-optional-chaining": "^7.0.0",
+    "@babel/plugin-proposal-optional-chaining": "^7.2.0",
     "@babel/plugin-transform-runtime": "^7.0.0",
     "@babel/preset-env": "^7.0.0",
     "@babel/preset-react": "^7.0.0",

src/core/components/layout-utils.jsx

@@ -186,7 +186,7 @@ export class Select extends React.Component {
 
   render(){
     let { allowedValues, multiple, allowEmptyValue, disabled } = this.props
-    let value = this.state.value.toJS ? this.state.value.toJS() : this.state.value
+    let value = this.state.value?.toJS?.() || this.state.value
 
     return (
       <select className={this.props.className} multiple={ multiple } value={value} onChange={ this.onChange } disabled={disabled} >

test/e2e-cypress/static/documents/bugs/5452/openapi.yaml

@@ -0,0 +1,20 @@
+openapi: "3.0.0"
+info:
+  title: Testcase API
+  version: 2.0.0
+paths:
+  '/endpoint':
+    get:
+      parameters:
+        - name: type
+          in: query
+          example: fruit
+          schema:
+            type: string
+            enum:
+              - fruit
+              - vegetable
+              - drink
+      responses:
+        '200':
+          description: 200 response

test/e2e-cypress/static/documents/bugs/5452/swagger.yaml

@@ -0,0 +1,19 @@
+swagger: "2.0"
+info:
+  title: Testcase API
+  version: 2.0.0
+paths:
+  '/endpoint':
+    get:
+      parameters:
+        - name: type
+          in: query
+          x-example: fruit
+          type: string
+          enum:
+            - fruit
+            - vegetable
+            - drink
+      responses:
+        '200':
+          description: 200 response

test/e2e-cypress/tests/bugs/5452.js

@@ -0,0 +1,34 @@
+/**
+ * @prettier
+ */
+
+describe("#5452: <Select /> crashing in Parameters", function() {
+  describe("in OpenAPI 3", () => {
+    it("should not result in a render error", function() {
+      cy.visit("http://localhost:3230/?url=/documents/bugs/5452/openapi.yaml")
+        .get("#operations-default-get_endpoint")
+        .click()
+        .get(".parameters > tbody > tr > .col > select")
+        .select("")
+        .get(".parameters > tbody > tr > .col > select")
+        .should("exist")
+        .select("fruit")
+        .get(".parameters > tbody > tr > .col > select")
+        .should("exist")
+    })
+  })
+  describe("in Swagger 2", () => {
+    it("should not result in a render error", function() {
+      cy.visit("http://localhost:3230/?url=/documents/bugs/5452/swagger.yaml")
+        .get("#operations-default-get_endpoint")
+        .click()
+        .get(".parameters > tbody > tr > .col > select")
+        .select("")
+        .get(".parameters > tbody > tr > .col > select")
+        .should("exist")
+        .select("fruit")
+        .get(".parameters > tbody > tr > .col > select")
+        .should("exist")
+    })
+  })
+})