Empty string cannot be passed in HttpTrigger query string

[lucyzhang929]

Repro steps

1. Run the following function from templates:

package com.function;

import java.util.*;
import com.microsoft.azure.functions.annotation.*;
import com.microsoft.azure.functions.*;

/**
 * Azure Functions with HTTP Trigger.
 */
public class HttpTriggerJava1 {
    /**
     * This function listens at endpoint "/api/HttpTriggerJava1". Two ways to invoke it using "curl" command in bash:
     * 1. curl -d "HTTP Body" {your host}/api/HttpTriggerJava1
     * 2. curl {your host}/api/HttpTriggerJava1?name=HTTP%20Query
     */
    @FunctionName("HttpTriggerJava1")
    public HttpResponseMessage run(
            @HttpTrigger(name = "req", methods = {HttpMethod.GET, HttpMethod.POST}, authLevel = AuthorizationLevel.FUNCTION) HttpRequestMessage<Optional<String>> request,
            final ExecutionContext context) {
        context.getLogger().info("Java HTTP trigger processed a request.");

        // Parse query parameter
        String query = request.getQueryParameters().get("name");
        String name = request.getBody().orElse(query);

        if (name == null) {
            return request.createResponseBuilder(HttpStatus.BAD_REQUEST).body("Please pass a name on the query string or in the request body").build();
        } else {
            return request.createResponseBuilder(HttpStatus.OK).body("Hello, " + name).build();
        }
    }
}

2. Send the following request: http://localhost:7071/api/HttpTriggerJava1?name=

Expected behavior

name should be set to an empty string and the function should return "Hello, "

Actual behavior

name is set to null and the function returns "Please pass a name on the query string or in the request body"

Known workarounds

None

Related information

Similar issue in PowerShell worker: Azure/azure-functions-powershell-worker#895