ADDITIONAL SYSTEM INFORMATION :
The compilation is tested on:
Linux 64bit - JDK11.0.4
Windows 32bit - JDK8u221


A DESCRIPTION OF THE PROBLEM :
For a precise code pattern, Java compiler makes a bad compilation result, giving null for a catched exception variable. In our production code, it causes NullPointerException when we evoke getMessage() method on it.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile the source code (the test code executes well; the original production code in the same circumstances causes a NullPointerException)

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Result of decompilation of compiled class:
public class ForCatchBug
{
  public static void methodWithException(int paramInt) throws Exception { if (paramInt == 1) throw new Exception("exception");
     }

  
  public static void main(String[] paramArrayOfString) {
    for (b = 0; b < 5; b++) {
      System.out.println(b);
    }
    try {
      methodWithException(1);
    } catch (Exception exception) {
      System.out.println(exception.getMessage());
    }
  }
}
ACTUAL -
Result of decompilation of compiled class:
public class ForCatchBug
{
  public static void methodWithException(int paramInt) throws Exception { if (paramInt == 1) throw new Exception("exception");
     }

  
  public static void main(String[] paramArrayOfString) {
    for (b = 0; b < 5; b++) {
      System.out.println(b);
    }
    try {
      methodWithException(1);
    } catch (Exception b) {
      Exception exception; System.out.println(exception.getMessage()); <=== Creation of a new variable
    }
  }
}

---------- BEGIN SOURCE ----------
import java.lang.Exception;

public class ForCatchBug {

  public static void methodWithException(int a) throws Exception {
    if (a == 1) throw new Exception("exception");
    return;
  }

  public static void main(String[] args) {
    for (int i = 0; i < 5; i++) {
      System.out.println(i);
    }
    try {
      methodWithException(1);
    } catch (Exception e) {
      System.out.println(e.getMessage());
    }
    return;
  }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
The problem disappears if the part of the code:
    for (int i = 0; i < 5; i++) {
is replaced by :
    int i = 0;
    for (i = 0; i < 5; i++) {