Geppetto plugin seems to cause failures opening a json file

[MarkRx]

Migrating over from https://github.com/eclipse/xtext-xtend/issues/239.

When I attempt to open a json file I get a dialog that says:

Unsupported Content Type To associate file extension with a supported content type, please see Content Types Preference Page

In the Content Types Preference Page JSON (Illformed) is associated with .json. In preferences General > Editors > File Associations *.json uses the JSON Editor

The eclipse log simply says this:

!ENTRY org.eclipse.wst.sse.ui 2 2 2017-07-28 08:08:44.255 !MESSAGE Input Name: bla.json

!ENTRY org.eclipse.wst.sse.ui 2 2 2017-07-28 08:08:44.256 !MESSAGE Unexpected IDocumentProvider implementation: org.eclipse.xtext.ui.editor.model.XtextDocumentProvider

!ENTRY org.eclipse.wst.sse.ui 2 2 2017-07-28 08:08:44.257 !MESSAGE Unexpected IDocument implementation: org.eclipse.xtext.ui.editor.model.XtextDocument

It appears to be a plugin conflict with the following plugins:

• Xtend plugin (?)
• Eclipse Web Developer Tools
• Geppetto for Eclipse IDE

  Eclipse DSL Tools	4.7.0.20170620-1800	epp.package.dsl	Eclipse Packaging Project
  Eclipse Web Developer Tools	3.9.0.v201706011953	org.eclipse.wst.web_ui.feature.feature.group	Eclipse Web Tools Platform
  EMF - Eclipse Modeling Framework SDK	2.13.0.v20170609-0928	org.eclipse.emf.sdk.feature.group	Eclipse Modeling Project
  EMF - Eclipse Modeling Framework Xcore SDK	1.5.0.v20170613-0242	org.eclipse.emf.ecore.xcore.sdk.feature.group	Eclipse Modeling Project
  Geppetto for Eclipse IDE	4.3.1.v20150119-0753	com.puppetlabs.geppetto.eclipse.ide.feature.group	Puppet Labs, Inc.
  Geppetto PuppetDB Integration	4.3.1.v20150117-1918	com.puppetlabs.geppetto.puppetdb.feature.group	Puppet Labs, Inc.
  LSP4J SDK	0.2.0.v20170518-0647	org.eclipse.lsp4j.sdk.feature.group	Eclipse LSP4J
  MWE 2 language SDK	2.9.1.201705291011	org.eclipse.emf.mwe2.language.sdk.feature.group	Eclipse Xtext
  Xtext Complete SDK	2.12.0.v20170519-1412	org.eclipse.xtext.sdk.feature.group	Eclipse Xtext

To reproduce:

1. Download Eclipse Oxygen DSL edition
2. Install Eclipse Web Developer Tools from the oxygen release site (http://download.eclipse.org/releases/oxygen)
3. Install Geppetto for Eclipse IDE (http://geppetto-updates.puppetlabs.com/4.x)
4. Open a json document. You will get the error mentioned above.