pipeline credential

def getTools() {
    stage("Get tool") {
        environment {
            GITHUB_CREDS = credentials('git') // actually an uuid from the .../jenkins/credentials/ page
        }
        sh '''
          mkdir -p tools 
        '''
        dir("tools") {
            checkout([
                $class: 'GitSCM', branches: [[name: '*/master']],
                doGenerateSubmoduleConfigurations: false,
                extensions: [
                    [$class: 'SparseCheckoutPaths',  sparseCheckoutPaths:[[$class:'SparseCheckoutPath', path:'some/path/']]]
                ],
                submoduleCfg: [],
                userRemoteConfigs: [[
                    credentialsId: "$GITHUB_CREDS",
                    url: '[email protected]:My/repos.git'
                ]]
            ])
        }
    }
}


===> 

groovy.lang.MissingPropertyException: No such property: GITHUB_CREDS for class: groovy.lang.Binding
	at groovy.lang.Binding.getVariable(Binding.java:63)
	at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onGetProperty(SandboxInterceptor.java:242)
	at org.kohsuke.groovy.sandbox.impl.Checker$6.call(Checker.java:282)
	at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:286)
	at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:262)
	at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:262)
	at com.cloudbees.groovy.cps.sandbox.SandboxInvoker.getProperty(SandboxInvoker.java:29)
	at com.cloudbees.groovy.cps.impl.PropertyAccessBlock.rawGet(PropertyAccessBlock.java:20)
	at WorkflowScript.getSignerTools(WorkflowScript:64)
	at ___cps.transform___(Native Method)