NPE in ImmutablesBuilderMissingInitialization

[laflechejonathan]

What happened?

     error-prone version: 2.4.0
     BugPattern: ImmutablesBuilderMissingInitialization
     Stack Trace:
     java.lang.NullPointerException: Cannot invoke "com.sun.source.tree.BlockTree.getStatements()" because the return value of "com.sun.source.tree.MethodTree.getBody()" is null
  	at com.palantir.baseline.errorprone.ImmutablesBuilderMissingInitialization.methodJustConstructsBuilder(ImmutablesBuilderMissingInitialization.java:244)
  	at com.palantir.baseline.errorprone.ImmutablesBuilderMissingInitialization.checkInitialization(ImmutablesBuilderMissingInitialization.java:170)
  	at com.palantir.baseline.errorprone.ImmutablesBuilderMissingInitialization.matchMethodInvocation(ImmutablesBuilderMissingInitialization.java:132)
  	at com.google.errorprone.scanner.ErrorProneScanner.processMatchers(ErrorProneScanner.java:451)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitMethodInvocation(ErrorProneScanner.java:748)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitMethodInvocation(ErrorProneScanner.java:152)
  	at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1761)
  	at jdk.compiler/com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:82)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:74)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:48)
  	at jdk.compiler/com.sun.source.util.TreeScanner.scan(TreeScanner.java:105)
  	at jdk.compiler/com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:113)
  	at jdk.compiler/com.sun.source.util.TreeScanner.visitMethodInvocation(TreeScanner.java:528)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitMethodInvocation(ErrorProneScanner.java:753)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitMethodInvocation(ErrorProneScanner.java:152)
  	at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1761)
  	at jdk.compiler/com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:82)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:74)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:48)
  	at jdk.compiler/com.sun.source.util.TreeScanner.visitExpressionStatement(TreeScanner.java:452)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitExpressionStatement(ErrorProneScanner.java:635)
  	at com.google.errorprone.scanner.ErrorProneScanner.visitExpressionStatement(ErrorProneScanner.java:152)
  	at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1540)
  	at jdk.compiler/com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:82)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:74)
  	at com.google.errorprone.scanner.Scanner.scan(Scanner.java:48)

The offending code looks roughly like:

private void doFoo(FooContext ctx) {
    doCoolThing(ctx.fooBuilder().build());
}