Could not find property 'RELEASE_STUDY_ID' when building this app #5

I downloaded this repo (zip), then extracted it,

Then cd to directory...

Then, ./gradlew assembleDebug

Unfortunately this error occur =

FAILURE: Build failed with an exception.

• Where:
  Build file '/home/din/TestAndroid/MoleMapperAndroid-master/app/build.gradle' line: 36

• What went wrong:
  A problem occurred evaluating project ':app'.

Could not find property 'RELEASE_STUDY_ID' on BuildType_Decorated{name=release, debuggable=false, testCoverageEnabled=false, jniDebuggable=false, pseudoLocalesEnabled=false, renderscriptDebuggable=false, renderscriptOptimLevel=3, versionNameSuffix=null, minifyEnabled=false, zipAlignEnabled=true, signingConfig=null, embedMicroApp=true, mBuildConfigFields={STUDY_BASE_URL=com.android.builder.internal.ClassFieldImpl@294947c5}, mResValues={}, mProguardFiles=[/home/din/Android/Sdk/tools/proguard/proguard-android.txt, /home/din/TestAndroid/MoleMapperAndroid-master/app/proguard-rules.pro], mConsumerProguardFiles=[], mManifestPlaceholders={}}.