fix errors with missing key and clef (#905)

src/MusicalScore/Graphical/MusicSystemBuilder.ts

@@ -396,11 +396,16 @@ export class MusicSystemBuilder {
                 const graphicalMeasure: GraphicalMeasure = this.graphicalMusicSheet
                     .getGraphicalMeasureFromSourceMeasureAndIndex(firstSourceMeasure, staffIndex);
                 this.activeClefs[i] = <ClefInstruction>firstSourceMeasure.FirstInstructionsStaffEntries[staffIndex].Instructions[0];
-                let keyInstruction: KeyInstruction = KeyInstruction.copy(
-                    <KeyInstruction>firstSourceMeasure.FirstInstructionsStaffEntries[staffIndex].Instructions[1]);
-                keyInstruction = this.transposeKeyInstruction(keyInstruction, graphicalMeasure);
-                this.activeKeys[i] = keyInstruction;
-                this.activeRhythm[i] = <RhythmInstruction>firstSourceMeasure.FirstInstructionsStaffEntries[staffIndex].Instructions[2];
+                const firstKeyInstruction: KeyInstruction = <KeyInstruction>firstSourceMeasure.FirstInstructionsStaffEntries[staffIndex].Instructions[1];
+                if (firstKeyInstruction) {
+                    let keyInstruction: KeyInstruction = KeyInstruction.copy(firstKeyInstruction);
+                    keyInstruction = this.transposeKeyInstruction(keyInstruction, graphicalMeasure);
+                    this.activeKeys[i] = keyInstruction;
+                }
+                const firstRhythmInstruction: RhythmInstruction = <RhythmInstruction>
+                    firstSourceMeasure.FirstInstructionsStaffEntries[staffIndex].Instructions[2];
+                // if (firstRhythmInstruction) {
+                this.activeRhythm[i] = firstRhythmInstruction;
             }
         }
     }

src/MusicalScore/Graphical/VexFlow/VexFlowConverter.ts

@@ -790,6 +790,8 @@ export class VexFlowConverter {
                 type = "treble";
                 break;
             default:
+                log.info("bad clef type: " + clef.ClefType);
+                type = "treble";
         }
 
         // annotations in vexflow don't allow bass and 8va. No matter the offset :(