When dealing with parametrized types, the value of "originalType" field in MXBean's descriptor may contain extra spaces. E.g. the present moment the type

  Map<String, Byte>

is represented in descriptor as "java.util.Map<java.lang.String, java.lang.Byte>".
While the spec says:
--
For a parameterized type such as Map<String,Integer> it is a string representation of the type, with the raw type followed by the actual type arguments in angle brackets separated by commas *without spaces*, for example "java.util.Map<java.lang.String,java.lang.Integer>".
--

The following code demonstrates the above-stated:
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/* Main.java */

import java.util.Map;
import javax.management.Descriptor;
import javax.management.JMX;
import javax.management.MBeanAttributeInfo;
import javax.management.MBeanInfo;
import javax.management.MBeanServer;
import javax.management.MBeanServerFactory;
import javax.management.ObjectName;

public class Main {
    
    public static void main(String[] args) {
        Main instance = new Main();
        
        instance.m1();
    }
    

    void m1() {
       try {
            MBeanServer mbs = MBeanServerFactory.newMBeanServer();
            ObjectName genericObjectName = new ObjectName("test:type=MapTypeMXBean");
            
            Test tst = new Test();
            mbs.registerMBean(tst, genericObjectName);

            MBeanInfo mbi = mbs.getMBeanInfo(genericObjectName);
            MBeanAttributeInfo[] mbai = mbi.getAttributes();
            
            for (int i=0; i<mbai.length; i++) {
                if (mbai[i].getName().equals("Map")) {
                    Descriptor desc = mbai[i].getDescriptor();
                    System.out.println("originalType: " + desc.getFieldValue(JMX.ORIGINAL_TYPE_FIELD));
                }
            }

        } catch (Throwable e) {
            e.printStackTrace();
        }
    }
    
    public interface TestMXBean {
        Map<String, Byte> getMap();
    }
    
    public static class Test implements TestMXBean {
        
        public Map<String, Byte> getMap() {
            return null;
        }
    }
}
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Output:
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...
run-single:
originalType: java.util.Map<java.lang.String, java.lang.Byte>
BUILD SUCCESSFUL (total time: 1 second)
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