fix: prevent panics in case of nils

[miparnisari]

Extracting some changes from #2965

[codecov]

Codecov Report

❌ Patch coverage is 77.35849% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.50%. Comparing base (ea6c5f2) to head (f9b79dd).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/caveats/parameters.go	0.00%	2 Missing and 1 partial ⚠️
pkg/schemadsl/compiler/compiler.go	40.00%	2 Missing and 1 partial ⚠️
pkg/schemadsl/compiler/importer.go	0.00%	2 Missing and 1 partial ⚠️
pkg/schemadsl/compiler/translator.go	88.47%	2 Missing and 1 partial ⚠️

❌ Your project status has failed because the head coverage (73.50%) is below the target coverage (75.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2971      +/-   ##
==========================================
- Coverage   74.83%   73.50%   -1.33%     
==========================================
  Files         498      498              
  Lines       61041    61058      +17     
==========================================
- Hits        45672    44872     -800     
- Misses      12178    12990     +812     
- Partials     3191     3196       +5     

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[miparnisari]

FYI this test in the position mapper makes it crash:

{
+                       name: "caveat parameter reference second reference",
+                       schema: `definition user {}
+
+                       caveat somecaveat(someparam int) {
+                               someparam < 42 || someparam > 43
+                       }
+
+                       definition resource {
+                               relation viewer: user with somecaveat
+                               permission view = viewer
+                       }
+                       `,
+                       line:   3,
+                       column: 23,
+                       expectedReference: &SchemaReference{
+                               Source:                   input.Source("test"),
+                               Position:                 input.Position{LineNumber: 3, ColumnPosition: 23},                                                                                              
+                               Text:                     "someparam",
+                               ReferenceType:            ReferenceTypeCaveatParameter,
+                               ReferenceMarkdown:        "someparam int",
+                               TargetSource:             &testSource,
+                               TargetSourceCode:         "someparam int",
+                               TargetNamePositionOffset: 0,
+                       },
+               },

[miparnisari]

FYI notice how the flags map isn't set