SCP task with ssh key authentication doesn't work if passphrase is empty

Error occurred while running Task 'Copy' of type com.atlassian.bamboo.plugins.bamboo-scp-plugin:scptask.
23-Feb-2018 13:24:03 java.lang.NullPointerException
23-Feb-2018 13:24:03 at com.atlassian.bamboo.plugins.scp.SSHKeyProvider.<init>(SSHKeyProvider.java:26)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.plugins.scp.ScpTask.execute(ScpTask.java:257)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.plugins.scp.ScpTask.run(ScpTask.java:120)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.plugins.scp.ScpTask.execute(ScpTask.java:106)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.task.TaskExecutorImpl.lambda$executeTasks$1(TaskExecutorImpl.java:281)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.task.TaskExecutorImpl.executeTaskWithPrePostActions(TaskExecutorImpl.java:224)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.task.TaskExecutorImpl.executeTasks(TaskExecutorImpl.java:281)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.task.TaskExecutorImpl.execute(TaskExecutorImpl.java:112)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.build.pipeline.tasks.ExecuteBuildTask.call(ExecuteBuildTask.java:71)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.v2.build.agent.DefaultBuildAgent.executeBuildPhase(DefaultBuildAgent.java:203)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.v2.build.agent.DefaultBuildAgent.build(DefaultBuildAgent.java:175)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.v2.build.agent.BuildAgentControllerImpl.lambda$waitAndPerformBuild$0(BuildAgentControllerImpl.java:122)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.variable.CustomVariableContextImpl.withVariableSubstitutor(CustomVariableContextImpl.java:185)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.v2.build.agent.BuildAgentControllerImpl.waitAndPerformBuild(BuildAgentControllerImpl.java:117)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.v2.build.agent.DefaultBuildAgent$1.run(DefaultBuildAgent.java:126)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.utils.BambooRunnables$1.run(BambooRunnables.java:48)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.security.ImpersonationHelper.runWith(ImpersonationHelper.java:26)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.security.ImpersonationHelper.runWithSystemAuthority(ImpersonationHelper.java:17)
23-Feb-2018 13:24:03 at com.atlassian.bamboo.security.ImpersonationHelper$1.run(ImpersonationHelper.java:41)
23-Feb-2018 13:24:03 at java.lang.Thread.run(Thread.java:748)