Jenkinsfile Shared Library

Jenkinsfile

@Library('jenkinsfile-library')
import com.foo.Methods

node {
  def m = new com.foo.Methods()
  def ip = m.getPublicIP()
  echo ip
}

Methods.groovy

#!/usr/bin/env groovy
package com.foo

class Methods implements Serializable {
  static def getPublicIP() {
    sh returnStdout: true, script: 'curl icanhazip.com'
  }
}

Error message from line 6 of Jenkinsfile:

hudson.remoting.ProxyException: groovy.lang.MissingMethodException: No signature of method: static com.foo.Methods.sh() is 
applicable for argument types: (java.util.LinkedHashMap) values: [[returnStdout:true, script:curl icanhazip.com]]
Possible solutions: is(java.lang.Object), use([Ljava.lang.Object;), any(), any(groovy.lang.Closure), 
each(groovy.lang.Closure), use(java.lang.Class, groovy.lang.Closure)