How to create a flow files and add attributes in a custom processor

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package com.demo.processors;

import org.apache.commons.lang3.StringUtils;
import org.apache.nifi.annotation.behavior.InputRequirement;
import org.apache.nifi.annotation.behavior.ReadsAttribute;
import org.apache.nifi.annotation.behavior.ReadsAttributes;
import org.apache.nifi.annotation.behavior.WritesAttribute;
import org.apache.nifi.annotation.behavior.WritesAttributes;
import org.apache.nifi.annotation.documentation.CapabilityDescription;
import org.apache.nifi.annotation.documentation.SeeAlso;
import org.apache.nifi.annotation.documentation.Tags;
import org.apache.nifi.annotation.lifecycle.OnScheduled;
import org.apache.nifi.components.PropertyDescriptor;
import org.apache.nifi.expression.ExpressionLanguageScope;
import org.apache.nifi.flowfile.FlowFile;
import org.apache.nifi.processor.ProcessContext;
import org.apache.nifi.processor.ProcessSession;
import org.apache.nifi.processor.ProcessorInitializationContext;
import org.apache.nifi.processor.util.StandardValidators;
import org.apache.nifi.processors.standard.InvokeHTTP;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

@Tags({"GetMember"})
@CapabilityDescription("Get a Member details from member collection")
@SeeAlso({})
@ReadsAttributes({@ReadsAttribute(attribute = "", description = "")})
@WritesAttributes({@WritesAttribute(attribute = "", description = "")})
@InputRequirement(InputRequirement.Requirement.INPUT_FORBIDDEN)
public class GetMemberProcessor extends InvokeHTTP {

    public static final PropertyDescriptor ID = new PropertyDescriptor
            .Builder().name("ID")
            .displayName("Id")
            .description("Member Id")
            .required(false)
            .addValidator(StandardValidators.NON_EMPTY_VALIDATOR)
            .build();
    
    private static final String CUSTOM_URL = "https://my-url/api/v1";
    private static final String GET_MEMBER_PATH = "/members";

    private List<PropertyDescriptor> descriptors;

    @Override
    protected void init(final ProcessorInitializationContext context) {
        super.init(context);
        List<PropertyDescriptor> invokeDescriptors = super.getSupportedPropertyDescriptors();
        descriptors = new ArrayList<>();
        if (invokeDescriptors != null) {
            for (PropertyDescriptor descriptor : invokeDescriptors) {
                if (descriptor.getName().equalsIgnoreCase("HTTP URL")) {
                    continue;
                }
                descriptors.add(descriptor);
            }
        }

        PropertyDescriptor HTTP_URL = new PropertyDescriptor.Builder()
                .name("HTTP URL")
                .description("Get Members URL")
                .required(false)
                .defaultValue(CUSTOM_URL + GET_MEMBER_PATH + "/${MEMBER_ID}")
                .expressionLanguageSupported(ExpressionLanguageScope.FLOWFILE_ATTRIBUTES)
                .addValidator(StandardValidators.URL_VALIDATOR)
                .build();


        descriptors.add(ID);
        descriptors.add(HTTP_URL);
        descriptors = Collections.unmodifiableList(descriptors);
    }

    @Override
    public final List<PropertyDescriptor> getSupportedPropertyDescriptors() {
        return descriptors;
    }

    @OnScheduled
    public void onScheduled(final ProcessContext context) {

    }

    @Override
    public void onTrigger(final ProcessContext context, final ProcessSession session) {
        String memberId = StringUtils.trimToEmpty(context.getProperty("ID").evaluateAttributeExpressions().getValue());
        String uri = StringUtils.trimToEmpty(context.getProperty("HTTP URL").evaluateAttributeExpressions().getValue());
        getLogger().info("ID: " + memberId + "  URI Found: " + uri);
        FlowFile requestFlowFile = session.get();
        if (requestFlowFile == null) {
            requestFlowFile = session.create();
        }
        session.putAttribute(requestFlowFile, "MEMBER_ID", memberId);
        String uri2 = StringUtils.trimToEmpty(context.getProperty("HTTP URL").evaluateAttributeExpressions().getValue());
        getLogger().info("ID: " + memberId + "  URI Found after: " + uri2);
        super.onTrigger(context, session);
    }
}

Hi all, I am new to nifi and trying to create a new custom processor extending the invokeHttp processor. I am trying to write a processor will some default values pre configured in to invokeHttp and ask my team to use this processor to add properties that will be used to update properties in the invokeHttp properties.

I am getting the following error while trying to run the custom processor