diff --git a/clean_files.txt b/clean_files.txt
index 0e6c39f5..8c8b3fed 100644
--- a/clean_files.txt
+++ b/clean_files.txt
@@ -97,6 +97,7 @@ plugins/available/history-search.plugin.bash
 plugins/available/history-substring-search.plugin.bash
 plugins/available/history.plugin.bash
 plugins/available/hub.plugin.bash
+plugins/available/java.plugin.bash
 plugins/available/jekyll.plugin.bash
 plugins/available/jump.plugin.bash
 plugins/available/less-pretty-cat.plugin.bash
diff --git a/plugins/available/java.plugin.bash b/plugins/available/java.plugin.bash
index 98e46247..2a80a99a 100644
--- a/plugins/available/java.plugin.bash
+++ b/plugins/available/java.plugin.bash
@@ -1,11 +1,11 @@
-cite about-plugin
+# shellcheck shell=bash
 about-plugin 'Java and JAR helper functions'
 
 function jar_manifest {
-  about "extracts the specified JAR file's MANIFEST file and prints it to stdout"
-  group 'java'
-  param '1: JAR file to extract the MANIFEST from'
-  example 'jar_manifest lib/foo.jar'
+	about "extracts the specified JAR file's MANIFEST file and prints it to stdout"
+	group 'java'
+	param '1: JAR file to extract the MANIFEST from'
+	example 'jar_manifest lib/foo.jar'
 
-  unzip -c $1 META-INF/MANIFEST.MF
+	unzip -c "${1:?${FUNCNAME[0]}: JAR file must be specified}" META-INF/MANIFEST.MF
 }