Apps: Fix broken GET/PUT/CREATE

[scblack321]

When retrieving an app (GET) it should be possible to use the result in a PUT or (with modified id) a CREATE.
This currently fails for CREATE if the app contains a null value for jobAttributes.fileInputs.envKey. Presumably PUT would fail also.

Example error message:

TAPIS_JSON_VALIDATION_ERROR JSON validation error: TAPIS_JSON_VALIDATION_FAILURE JSON validation error: #/jobAttributes: #: no subschema matched out of the total 1 subschemas #1#/jobAttributes/fileInputs: expected: null, found: JSONArray #2#/jobAttributes/fileInputs/0/envKey: expected type: String, found: Null #3#/jobAttributes/fileInputs/1/envKey: expected type: String, found: Null #4#/jobAttributes/fileInputs/2/envKey: expected type: String, found: Null #5#/jobAttributes/fileInputs/3/envKey: expected type: String, found: Null #6#/jobAttributes/fileInputs/4/envKey: expected type: String, found: Null #7#/jobAttributes/fileInputs/5/envKey: expected type: String, found: Null