RFR: 7246: ClassCastException when opening heap dump

[Tobias Stadler]

Signed-off-by: Tobias Stadler <ts.stadler at gmx.de>

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Commit messages:
 - 7246: ClassCastException when opening heap dump

Changes: https://git.openjdk.java.net/jmc/pull/243/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=243&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-7246
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jmc/pull/243.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/243/head:pull/243

PR: https://git.openjdk.java.net/jmc/pull/243