cache: guard null fields in Entry.writeTo() to fix NPE (#8962)

okhttp/src/commonJvmAndroid/kotlin/okhttp3/Cache.kt

@@ -628,9 +628,9 @@ class Cache internal constructor(
           .writeDecimalLong(receivedResponseMillis)
           .writeByte('\n'.code)
 
-        if (url.isHttps) {
+        if (url.isHttps && handshake != null) {
           sink.writeByte('\n'.code)
-          sink.writeUtf8(handshake!!.cipherSuite.javaName).writeByte('\n'.code)
+          sink.writeUtf8(handshake.cipherSuite.javaName).writeByte('\n'.code)
           writeCertList(sink, handshake.peerCertificates)
           writeCertList(sink, handshake.localCertificates)
           sink.writeUtf8(handshake.tlsVersion.javaName).writeByte('\n'.code)

okhttp/src/jvmTest/kotlin/okhttp3/CacheTest.kt

@@ -422,6 +422,134 @@ class CacheTest {
       .close()
   }
 
+  /**
+   * A network interceptor strips the handshake from a real HTTPS response before the
+   * CacheInterceptor writes it to disk. This creates the bug condition: url.isHttps=true
+   * but handshake=null. Before the fix, `handshake!!` in writeTo() threw NPE.
+   *
+   * https://github.com/square/okhttp/issues/8962
+   */
+  @Test
+  fun httpsResponseWithNullHandshakeDoesNotCrashWriteTo() {
+    server.useHttps(handshakeCertificates.sslSocketFactory())
+    server.enqueue(
+      MockResponse
+        .Builder()
+        .body("secure content")
+        .addHeader("Cache-Control", "max-age=3600")
+        .build(),
+    )
+
+    client =
+      client
+        .newBuilder()
+        .sslSocketFactory(
+          handshakeCertificates.sslSocketFactory(),
+          handshakeCertificates.trustManager,
+        ).hostnameVerifier(NULL_HOSTNAME_VERIFIER)
+        .addNetworkInterceptor { chain ->
+          chain
+            .proceed(chain.request())
+            .newBuilder()
+            .handshake(null)
+            .build()
+        }.build()
+
+    val response = client.newCall(Request(server.url("/"))).execute()
+    assertThat(response.code).isEqualTo(200)
+    assertThat(response.body.string()).isEqualTo("secure content")
+  }
+
+  /**
+   * Verifies the null-handshake fix holds across multiple sequential cache writes, confirming
+   * it is not a one-time race condition.
+   *
+   * https://github.com/square/okhttp/issues/8962
+   */
+  @Test
+  fun multipleHttpsRequestsWithNullHandshakeAllSucceed() {
+    server.useHttps(handshakeCertificates.sslSocketFactory())
+    repeat(3) {
+      server.enqueue(
+        MockResponse
+          .Builder()
+          .body("response $it")
+          .addHeader("Cache-Control", "max-age=3600")
+          .build(),
+      )
+    }
+
+    client =
+      client
+        .newBuilder()
+        .sslSocketFactory(
+          handshakeCertificates.sslSocketFactory(),
+          handshakeCertificates.trustManager,
+        ).hostnameVerifier(NULL_HOSTNAME_VERIFIER)
+        .addNetworkInterceptor { chain ->
+          chain
+            .proceed(chain.request())
+            .newBuilder()
+            .handshake(null)
+            .build()
+        }.build()
+
+    repeat(3) { i ->
+      val response = client.newCall(Request(server.url("/path$i"))).execute()
+      assertThat(response.code).isEqualTo(200)
+      assertThat(response.body.string()).isEqualTo("response $i")
+    }
+  }
+
+  /**
+   * When handshake is null for an HTTPS URL, the TLS block is skipped making the entry
+   * unreadable on re-read. The response should still succeed but won't be served from cache
+   * on subsequent requests.
+   *
+   * https://github.com/square/okhttp/issues/8962
+   */
+  @Test
+  fun httpsResponseWithNullHandshakeIsNotServedFromCache() {
+    server.useHttps(handshakeCertificates.sslSocketFactory())
+    server.enqueue(
+      MockResponse
+        .Builder()
+        .body("first")
+        .addHeader("Cache-Control", "max-age=3600")
+        .build(),
+    )
+    server.enqueue(
+      MockResponse
+        .Builder()
+        .body("second")
+        .addHeader("Cache-Control", "max-age=3600")
+        .build(),
+    )
+
+    client =
+      client
+        .newBuilder()
+        .sslSocketFactory(
+          handshakeCertificates.sslSocketFactory(),
+          handshakeCertificates.trustManager,
+        ).hostnameVerifier(NULL_HOSTNAME_VERIFIER)
+        .addNetworkInterceptor { chain ->
+          chain
+            .proceed(chain.request())
+            .newBuilder()
+            .handshake(null)
+            .build()
+        }.build()
+
+    val response1 = client.newCall(Request(server.url("/"))).execute()
+    assertThat(response1.body.string()).isEqualTo("first")
+
+    // Second request hits the network again because the first entry was not cacheable
+    val response2 = client.newCall(Request(server.url("/"))).execute()
+    assertThat(response2.body.string()).isEqualTo("second")
+    assertThat(response2.cacheResponse).isNull()
+  }
+
   @Test
   fun responseCachingAndRedirects() {
     server.enqueue(