Once users open their existing projects or create a new project in Android Studio 3.1, Gradle creates a Java serialized object file "build_file_checksums.ser" in folder ".idea/caches/".

The serialized object appears to include a string like "/Users/qtmfld/.gradle/gradle.properties". It's an absolute path in my Mac home directory.
https://stackoverflow.com/questions/49557737/

Users should avoid to commit such a file into their repositories.
https://www.google.co.jp/search?q=build_file_checksums.ser+site%3Agithub.com

I hope that the default .gitignore of Android Studio could ignore it in future versions.
https://issuetracker.google.com/36972204
"/Applications/Android Studio.app/Contents/plugins/android/lib/templates/gradle-projects/NewAndroidProject/root/project_ignore"
https://android.googlesource.com/platform/tools/base/+/studio-master-dev/templates/gradle-projects/NewAndroidProject/root/project_ignore

Steps to Reproduce:
1. Create a new project ( or open existing projects ) in Android Studio 3.1
2. Change the project window from "Android" to "Project"
3. Open ".idea/caches" and you will find "build_file_checksums.ser" (screenshot #1)
4. Enable Version Control Integration and choose Git
5. Commit changes and you will see "build_file_checksums.ser" (screenshot #2)

Build: 3.1, AI-173.4670197, 201803220120,

AI-173.4670197, JRE 1.8.0_152-release-1024-b01x64 JetBrains s.r.o, OS Mac OS X(x86_64) v10.13.3 unknown, screens 1440x900

Android Gradle Plugin: 3.1.0
Gradle: 4.4
NDK: from local.properties: (not specified); latest from SDK: (not found);
LLDB: pinned revision 3.1 not found; latest from SDK: (package not found);
CMake: from local.properties: (not specified); latest from SDK: (not found); from PATH: (not found);