Remove source compatibility with JDK 8

remove JDK 8 from external CI, and add a use of a JDK 11 API
(Optional.isEmpty) to confirm.

#2730

PiperOrigin-RevId: 415040230

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ ubuntu-latest ]
-        java: [ 17, 11, 8 ]
+        java: [ 17, 11 ]
         experimental: [ false ]
         # Only test on macos and windows with a single recent JDK to avoid a
         # combinatorial explosion of test configurations.
@@ -63,10 +63,10 @@ jobs:
     steps:
       - name: 'Check out repository'
         uses: actions/checkout@v2
-      - name: 'Set up JDK 8'
+      - name: 'Set up JDK 11'
         uses: actions/setup-java@v2
         with:
-          java-version: 8
+          java-version: 11
           distribution: 'zulu'
           cache: 'maven'
           server-id: ossrh

core/src/main/java/com/google/errorprone/bugpatterns/inlineme/Inliner.java

@@ -147,7 +147,7 @@ private Description match(
       ExpressionTree receiver,
       VisitorState state) {
     Optional<InlineMeData> inlineMe = InlineMeData.createFromSymbol(symbol);
-    if (!inlineMe.isPresent()) {
+    if (inlineMe.isEmpty()) {
       return Description.NO_MATCH;
     }