how to add custom environment variables to use in build.gradle in Androidd Studio

I have build.gradle setup with signingConfigs as below:

 SystemConfig90 {
            storeFile file(System.getenv("KEYSTORE_PATH_90"))
            //storeFile file('/Users/bhaskarrajaryal/AndroidStudioProjects/ATS/Keystore/90.keystore')
            storePassword '123456!'
            keyAlias '123456'
            keyPassword '123456'
        }

I tried to setup the KEYSTORE_PATH_90 inside Run → Edit Configurations and from there selecting the Gradle options and Adding Environment as key value pairs. The problem is that its showing null for the path.

Caused by: java.lang.IllegalArgumentException: path may not be null or empty string. path='null'
    at org.gradle.api.internal.file.AbstractBaseDirFileResolver.doResolve(AbstractBaseDirFileResolver.java:59)
    at org.gradle.api.internal.file.AbstractFileResolver.resolve(AbstractFileResolver.java:74)
    at org.gradle.api.internal.file.AbstractFileResolver.resolve(AbstractFileResolver.java:48)
    at org.gradle.api.internal.file.DefaultFileOperations.file(DefaultFileOperations.java:138)
    at org.gradle.groovy.scripts.DefaultScript.file(DefaultScript.java:148)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(Unknown Source)
    at org.gradle.internal.metaobject.BeanDynamicObject$MetaClassAdapter.invokeMethod(BeanDynamicObject.java:541)
    at org.gradle.internal.metaobject.BeanDynamicObject.tryInvokeMethod(BeanDynamicObject.java:218)
    at org.gradle.groovy.scripts.BasicScript$ScriptDynamicObject.tryInvokeMethod(BasicScript.java:134)
    at org.gradle.internal.metaobject.ConfigureDelegate.invokeMethod(ConfigureDelegate.java:79)
    at org.gradle.internal.metaobject.BeanDynamicObject$GroovyObjectAdapter.invokeOpaqueMethod(BeanDynamicObject.java:641)
    at org.gradle.internal.metaobject.BeanDynamicObject$MetaClassAdapter.invokeMethod(BeanDynamicObject.java:568)
    at org.gradle.internal.metaobject.BeanDynamicObject.tryInvokeMethod(BeanDynamicObject.java:218)
    at org.gradle.internal.metaobject.ConfigureDelegate.invokeMethod(ConfigureDelegate.java:79)
    at org.gradle.internal.metaobject.BeanDynamicObject$GroovyObjectAdapter.invokeOpaqueMethod(BeanDynamicObject.java:641)
    at org.gradle.internal.metaobject.BeanDynamicObject$MetaClassAdapter.invokeMethod(BeanDynamicObject.java:568)
    at org.gradle.internal.metaobject.BeanDynamicObject.tryInvokeMethod(BeanDynamicObject.java:218)
    at org.gradle.internal.metaobject.ConfigureDelegate.invokeMethod(ConfigureDelegate.java:79)
    at build_5n6psh1as86ozmlm2qewjl0d3$_run_closure1$_closure3$_closure8.doCall$original(/Users/bhaskarrajaryal/AndroidStudioProjects/ATS.Everalert.ClockApp/app/build.gradle:29)

But, if I keep the path static in Gradle file it's working. Am I adding this properly? Note: I am using Mac device