call MVEL.setProperty() method by parameter type error

package test;
public class MvelContext {
private String[] regkeys;
public void setRegkeys(String[] regkeys)

{this.regkeys = regkeys;}
public void setRegkeys(String regkey) {this.regkeys = regkey.split(",");}
}
public class MvelContextTest {
@Test
public void testname() throws Exception { MvelContext mvelContext = new MvelContext(); MVEL.setProperty(mvelContext, "regkeys", "s"); }
}

throws org.mvel.ConversionException: unable to resolve property: cannot convert type: class java.lang.String: to class [Ljava.lang.String;
at org.mvel.PropertyAccessor.set(PropertyAccessor.java:267)
at org.mvel.PropertyAccessor.set(PropertyAccessor.java:140)
at org.mvel.MVEL.setProperty(MVEL.java:575)
at test.MvelContextTest.testname(MvelContextTest.java:12)

when I change the order of this two methods in class test.MvelContext .
public class MvelContext {
private String[] regkeys;
public void setRegkeys(String regkey) {this.regkeys = regkey.split(",");}
public void setRegkeys(String[] regkeys) {this.regkeys = regkeys;}

}
It works fine.