drools-eclipse/org.drools.eclipse/src/main/java/org/drools/eclipse/reteoo/AlphaNodeVertex.java
public String getFieldName() {
        AlphaNodeFieldConstraint constraint = this.node.getConstraint();
        if (constraint instanceof MvelConstraint) {
        	MvelConstraint mvelConstraint = (MvelConstraint) constraint;
            InternalReadAccessor accessor = mvelConstraint.getFieldExtractor();
            if (accessor instanceof ClassFieldReader) {
                return ((ClassFieldReader) accessor).getFieldName();
            }
        }
        return null;
    }
public String getFieldName() {
        AlphaNodeFieldConstraint constraint = this.node.getConstraint();
        if (constraint instanceof MvelConstraint) {
        	MvelConstraint mvelConstraint = (MvelConstraint) constraint;
            InternalReadAccessor accessor = mvelConstraint.getFieldExtractor();
            if (accessor instanceof ClassFieldReader) {
                return ((ClassFieldReader) accessor).getFieldName();
            }
        }
        return null;
    }
Constraint has field extractor and this method is returning fieldName
it.

@return field name