Make sure ejbc task handles situation when build.compiler is not set

I didn't use Jeremy's patch directly since ejbcHelper is only interested if
build.compielr is equal to Jikes

Submitted by:	Jeremy Taylor <jtaylor@lehman.com>


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@268101 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/taskdefs/optional/ejb/EjbcHelper.java

@@ -318,7 +318,7 @@ public class EjbcHelper implements Ejbc.Helper {
         String compiler = project.getProperty("build.compiler");
         String[] args = null;
         
-        if (compiler.equalsIgnoreCase("jikes")) {
+        if (compiler != null && compiler.equalsIgnoreCase("jikes")) {
             Path execClassPath = new Path(project);
             if (Project.getJavaVersion() == Project.JAVA_1_1) {
                 execClassPath.addExisting(new Path(project, System.getProperty("java.home")