build: Fix search when generating Javadoc with broken java versions

api/build.gradle

@@ -96,6 +96,11 @@ javadoc {
 
     // Mark sources as Java 8 source compatible
     options.source = '8'
+
+    // Remove 'undefined' from seach paths when generating javadoc for a non-modular project (JDK-8215291)
+    if (JavaVersion.current() >= JavaVersion.VERSION_1_9 && JavaVersion.current() < JavaVersion.VERSION_12) {
+        options.addBooleanOption('-no-module-directories', true)
+    }
 }
 
 test {