com.sun.jdi.InvocationException occurred invoking method in JDK8

I am migrating my application from JDK 7 to JDK 8. While doing, I am facing an exception com.sun.jdi.InvocationException occurred invoking method when an instance of TestField as shown below is created. I am getting the exception while debugging and could not find the reason for it. I suspect NullPointerException occurs and InvocationException masks it. I have the below Object methods overridden in TestField.

Below utility classes are a part of commons-lang jar.

HashCodeBuilder
EqualsBuilder
ToStringBuilder

public class TestField {

private String name;

private Rules rules;

public TestField(String name, Rules rules)

{   this.name = name;
    this.rules = rules;
}

public String toString() {
    return new ToStringBuilder(this)
    .append("\n name", this.getName())
    .append("\n Rules", this.getRules())
    .append("\n ")
    .toString();
}

public boolean equals(Object other) {
    if ( !(other instanceof TestField) ) return false;
    TestField castOther = (TestField) other;
    return new EqualsBuilder()
        .append(this.getName(), castOther.getName())
                .append(this.getRules(), castOther.getRules())
        .isEquals();
}

public int hashCode() {
    return new HashCodeBuilder()
        .append(this.getName())            
        .append(this.getRules())            
        .toHashCode();
}   
}

Have anyone faced such an issue. Could anyone please help me to resolve the same. Thanks.