Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve project :sample.

[LizzyLi312]

Error:Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve project :sample.
There are also some problems like this. I'll show down below.
Error:Unable to resolve dependency for ':app@release/compileClasspath': Could not resolve project :sample.
Error:Unable to resolve dependency for ':app@releaseUnitTest/compileClasspath': Could not resolve project :sample.
Is there something missing in my build.gradle code? Here's the code of the buildtype part.
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
Thanks in advanced.