jqno#232: fixes NPE when verifying interfaces

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 ### Fixed
+- Verifying interfaces directly causes NullPointerException. ([Issue 232](/~https://github.com/jqno/equalsverifier/issues/232))
 - Improved error messages regarding JPA's `@EmbeddedId` annotation. ([Issue 231](/~https://github.com/jqno/equalsverifier/issues/231))
 
 

src/main/java/nl/jqno/equalsverifier/EqualsVerifierApi.java

@@ -339,7 +339,7 @@ private String buildErrorMessage(String description) {
     }
 
     private void performVerification() {
-        if (type.isEnum()) {
+        if (type.isEnum() || type.isInterface()) {
             return;
         }
 

src/test/java/nl/jqno/equalsverifier/integration/extended_contract/InterfaceTest.java

@@ -0,0 +1,20 @@
+package nl.jqno.equalsverifier.integration.extended_contract;
+
+import nl.jqno.equalsverifier.EqualsVerifier;
+import org.junit.Test;
+
+public class InterfaceTest {
+    @Test
+    public void succeed_whenClassIsAnInterface() {
+        EqualsVerifier.forClass(CharSequence.class)
+            .verify();
+    }
+
+    @Test
+    public void succeed_whenClassIsAnEmptyInterface() {
+        EqualsVerifier.forClass(Interface.class)
+            .verify();
+    }
+
+    interface Interface {}
+}